Aves

Snively, Eric & Russell, Anthony P., 2007, Functional morphology of neck musculature in the Tyrannosauridae (Dinosauria, Theropoda) as determined via a hierarchical inferential approach, Zoological Journal of the Linnean Society 151 (4), pp. 759-808 : 775-784

Aves : m. longus colli dorsalis

In birds m. longus colli dorsalis is a complex system involved in neck dorsiflexion ( Fig. 8A ). It is divided into two major components – posterior and anterior, m. longus colli dosalis pars caudalis and m. longus colli dosalis pars cranialis. Collectively these muscles form large paired, fusiform masses that originate at the base of the neck ( Figs 8 , 9B, D ). Their anteriormost extents ( Fig. 9A ) are the insertions of m. longus colli dorsalis pars anterior onto the epipophyses of the axis. The muscles are bound dorsally and laterally by a sheath of fascia (along with m. biventer cervicis), and contract and act on tendons of insertion within this sleeve. The profile of the posterior neck therefore follows the curve of the vertebrae, instead of filling out the entire dorsal concavity of this region.

M. longus colli dorsalis pars caudalis (m. l.c.d. caud.)

Origin: M. longus colli dorsalis pars caudalis ultimately originates from the aponeurosis notarii, arising from the neural arches and transverse processes of the anterior thoracic vertebrae and the last 1–3 cervical vertebrae, or tendinous slips arising from processes in this region ( Fig. 9D ). Slips diverge from a dorsal tendon or muscle mass lateral to the m. biv. c., and are often suspended within fascia when separated from surrounding muscles.

Insertion: Usually slips of m. l.c.d. caud. insert medially to mm. cervicales ascendentes on the processes dorsales of the posterior cervicals, in the dorsally concave region of the neck ( Fig. 9D ). However, they may share a tendon of insertion with a given m. cervicalis ascendens (as in the dissected Pelicanus occidentalis ) or even merge with bellies of mm. cervicales ascendentes (as in one adult specimen of Struthio camelus ).

M. longus colli dosalis pars cranialis (m. l.c.d. cran.)

Origin: M. longus colli dorsalis pars cranialis originates from the aponeurosis notarii or tendinously from neural spines of the cervicodorsal region ( Fig. 9B ), and is fairly massive and fusiform where it is separable from the posterior part of m. longus colli dorsalis pars caudalis ( Fig. 8A ). Other slips arise from epipophyses (processes dorsales) of cervicals from the posterior portion of the neck, medial to the insertions of m. l.c.d. caud. and mm. cervicales ascendentes ( Fig. 9C ), and from epipophyses of some more anterior vertebrae.

Insertion: M. l.c.d. cran. inserts tendinously far anteriorly from its posterior origin, onto a posteriorly concave surface of the epipophysis of C2, and rarely C3 ( Fig. 9A ), or onto the dorsal surface of these processes. The anterior slips of the muscle insert on this tendon as well. They thus run anterodorsally from a bony origin, contrasting with slips of m. l.c.d. caud. that run anteroventrally towards the posterior epipophyses as they diverge ventrally from the main belly of the muscle.

Crocodylia : M. transversospinalis cervicis (m. trans. cerv.) ( Tsuihiji, 2005; m. longissimus cervicis: Cong et al., 1998). M. longissimus cervicis (m. long. cerv.)/m. interarticulares ( Cleuren & De Vree, 2000; Tsuihiji, 2005)

These muscles have a confused nomenclature. They insert anteriorly at the same location, but are clearly discrete systems. They are treated together here.

Origin: In Alligator mississippiensis and Caiman crocodylus m. transversospinalis cervicis originates from the lateral surfaces of the neural spines ventral to the origins of m. transversospinalis capitis and m. spinocapitis posticus ( Fig. 6A ), and just anterior to the postzygapophyses of C3–C9 ( Fig. 6A ), by way of aponeuroses associated with the intermuscular septum that divides transversospinalis from longissimus systems. M. longissimus cervicis has similar aponeurotic origins from C4–C7 or C8, but also arises from the prezygapophyses of C4–C7 ( Fig. 9E ).

Insertion: M. trans. cerv. and m. long. cerv. insert on the posterodorsal portion of the postzygapophysis of C1 ( Fig. 9F ). M. trans. cerv. also inserts posteriorly on slightly raised scars in this position on the postzygapophyses of C3 and C4 ( Fig. 9F ). The postzygapophyseal insertion is similar to the insertion of m. longus colli dorsalis pars cranialis of birds. However, these muscles of crocodilians bypass C2, the site of the most prominent insertion in birds.

The name m. longissimus cervicis associates this muscle with the longissimus system, and Frey (1988) and Cong et al. (1998) do not differentiate m. long. cerv. from m. trans cerv. These are reasonable assignations, given that the muscles run together lateral to the neural arches, and have somewhat lateral insertions. However, because the origins of both muscles are from the base of the neural arch and not the transverse processes, they belong topologically to the transversospinalis system rather than the more ventrolaterally placed longissimus group.

Action/function: In birds multiple slips of m. l.c.d promote dorsiflexion of each postatlantal cervical relative to the immediately posterior vertebra. The tendinous insertion of m. l.c.d. cran. on the axis facilitates dorsiflexion of the entire ventrally concave anterior portion of the neck. EMG activity indicates a damping function during neck ventroflexion in chickens and ducks, and strong functions in neck retraction and dorsiflexion ( van der Leeuw et al., 2001). In crocodilians m. trans. cerv. is in a position to dorsiflex the neck, an activity aided by the neck’s dorsally concave curvature. EMG activity in crocodilians confirms strong neck dorsiflexive action of this muscle ( Cleuren & De Vree, 2000). The function of m. long. cerv./m. interarticulares have not been tested by EMG.

B. M. longissimus system

M. longissimus capitis superficialis (m. long. cap. sup.) ( Crocodylia )

As discussed, the ventral portion of m. complexus of birds, arising from the lateral tubercles of the transverse processes and sometimes inserting fleshily on the paroccipital processes, may be the homologue of m. longissimus capitis superficialis of crocodilians. Unlike this muscle in crocodilians, the ventral m. complexus of birds is anteriorly restricted to C1–C4. This homology is tentative, because the ventral portion of the body of m. complexus occurs only in some birds, and is continuous with the dorsal part. In contrast the crocodilian m. long. cap. sup. is a large discrete muscle, and is described in detail here. Its morphology is depicted in Figure 10B .

Origin: In Caiman crocodylus and Alligator mississippiensis , m. long. cap. sup. originates from the parapophyses and ventrolateral extent of the neural arches of C5–C9 ( Fig. 6A ), dorsomedial to the origins of m. longissimus capitis profundus on C5–C7. On C8 and C9 the origins of m. long. cap. sup. origin extend ventrolaterally to cover the distal surface of the parapophysis. The origin was tendinous from C 9 in the juvenile Alligator mississippiensis .

Insertion: The insertion of m. long. cap. sup. of crocodilians is tendinous onto the lateral extremity of the paroccipital process ( Fig. 6B ), ventral to the origin of m. depressor mandibulae and dorsolateral to the insertion of m. rectus capitis lateralis. The scar is rugose in most specimens.

Action/function: Having the lateralmost insertion of any craniocervical muscle in crocodilians, m. longissimus capitis superficialis is kinematically positioned to impart a strong, laterally flexive moment on the skull relative to the neck. EMG reveals strong activity of m. long. cap. sup. during head lateral flexion on the ipsilateral side of the neck ( Cleuren & De Vree, 2000), with very little or no damping activity by the contralateral muscle.

M. rectus capitis dorsalis (m. r.c.d.) ( Aves). M. longissimus capitis profundus (m. long. cap. prof.) (Crododylia)

Origin: In birds, m. rectus capitis dorsalis ( Fig. 10A ) typically originates from the anterolateral surface of C1, and the costal processes of the transverse processes of C1–C6 ( Fig. 5B ). In crocodilians, m. longissimus capitis profundus originates from the transverse processes just dorsal to their articulations with the cervical ribs ( Fig. 6A ).

Insertion: In both birds and crocodilians these muscles insert on the basioccipital, ventrolateral to the occipital condyle in crocodilians, and anteroventrolateral in birds ( Figs 4C , 5B ). The scar can be rugose in large crocodilians and birds, such as the dissected Caiman crocodylus and adult Struthio camelus , and on skulls of Alligator mississippiensis and Crocodylus acutus.

Action/function: In both crocodilians and birds m. r.c.d./m. long. cap. prof. insert ventral to the occipitial condyle, and are ideally positioned for head ventroflexion relative to the neck. EMG of crocodilians ( Cleuren & De Vree, 2000) confirms that the muscle is strongly active during this activity.

Mm. intertransversarii (mm. intertrans.) ( Vanden Berge & Zweers, 1993; Cong et al., 1998) ( Aves, Crocodylia , Varanidae ). Mm. inclusii ( Aves)

Mm. intertransversarii ( Figs 8A , 11 ) run between consecutive transverse processes in Aves, Crocodylia and Varanidae , and are here considered to be uniarticular

m. spl. cap. m. complexus m. r.c.d. (lateral)

(lateral)

components of the longissimus system. In this description the posterior transverse process of each pair is considered the origin, and the anterior one the insertion. This is not a universal practice in the literature ( Zusi & Storer, 1969), but the anterior vertebrae are less massive than posterior ones and are likely to be displaced more by contraction of mm. intertrans. ‘Insertion’ is a more appropriate designation for an attachment on the element that moves over greater excursion relative to the body’s centre of mass.

Mm. intertrans. vary substantially in extant sauropsids ( Figs 8A , 11 ). As described by Cong et al. (1998) they are dorsoventrally relatively thick bands in crocodilians, but are more dorsoventrally depressed in Varanus dumerilii . In birds these muscles are intricately subdivided and vary along the neck and among taxa. Only some of this variation is described here. Mm. inclusii, the medialmost components of this system, are present as short bellies in the posterior, dorsally concave portion of the neck.

Origin: In Aves bellies of mm. intertransversarii originate by aponeuroses from the lateral and dorsolateral tubercles ( Fig. 11A ). The origins are more discrete in the anterior portion of the neck, although dorsally the aponeuroses must sometimes be dissected free of superficial aponeuroses of origin for other muscles. In the posterior part of the neck, aponeuroses of mm. inclusii originate from the anterior face of the costal prosesses of birds ( Fig. 11B ). In crocodilians, the fleshy origins of m. intertrans. are deep and arise from along the anterior face of the transverse processes ( Fig. 11C ). In Varanus dumerilii the origin is dorsoventrally shallower than it is in crocodilians, and is ventrolaterally restricted on the transverse process.

Insertion: In birds the insertions (anterior attachments) of m. intertransversarii are aponeurotic onto the lateral tubercles of the transverse processes ( Fig. 11A ). Anteriorly, aponeuroses of mm. intertrans. to the dorsal and ventral lateral tubercles are separate, but posteriorly on the neck these aponeruroses appear to be conjoined dorsoventrally. In the anterior, dorsally convex portion of the neck in some taxa, long superficial bellies insert on the costal process of a vertebra, several cervicals anterior to the origin. This is an exception to the usually uniarticular morphology of the muscles. In the posterior portion of the neck, mm. inclusii insert on the lateral and dorsolateral crests of the posterior neural arch ( Fig. 11B ). In crocodilians and Varanus dumerilii the insertions of m. intertransversarii are fleshy onto the transverse process of the anterior vertebrae of each pair ( Fig. 11C ).

Action/function: In extant archosaurs and Varanus dumerilii , mm. intertrans. are positioned to laterally flex pairs of vertebrae relative to each other. The muscles are especially important for this function in birds, which lack the capacity for laterally flexing the entire neck by large superficial longissimus muscles present in other reptiles. Mm. intertrans. of birds spanning caudal vertebral joints are probably those most strongly involved in lateroflexion of the neck ( Heidweiller et al., 1992). In both crocodilians and varanids the transverse processes are laterally (and somewhat ventrally) extensive, indicating the capacity of effective intervertebral lateroflexion. Bilateral contraction might conceivably stabilize the intervertebral joints.

Interestingly, EMG of dorsal slips of anterior mm. intertrans. of adult chickens ( Heidweiller et al., 1992) shows intense activity during intervertebral dorsiflexion. This compensates for other neck dorsiflexors, which have proportionally smaller cross-sectional area than they do in juveniles ( Heidweiller et al., 1992).

C. M. iliocostalis and m. longus systems M. rectus capitis lateralis (m. r.c.l.) ( Vanden Berge & Zweers, 1993; Cong et al., 1998). Aves, Crododylia M. iliocostalis capitis (m. il. cap.) ( Seidel, 1978; Cleuren & De Vree, 2000). Crocodylia

Origin: In birds, m. rectus capitis lateralis ( Fig. 10A ) originates from the lateral surface of an enlarged hypopophysis of C2 ( Fig. 12A, B ) posterior to the origins of m. rectus capitis ventralis, or from the ventrolateral surface of the centrum. In dissected birds m. r.c.l. never originated from the costal process of C2, homologous with the vertebra’s cervical rib in other amniotes. This represents a dramatic medial shift from the muscle’s likely plesiomorphic origin in Archosauria that is retained in crocodilians.

In Caiman crocodylus and Alligator mississippiensis , m. iliocostalis capitis ( Cleuren & De Vree, 2000)/m. r.c.l. ( Cong et al., 1998) originates ventrally from strong white fascia surrounding ribs of C1 and C2 ( Fig. 6A ). Because the C1 rib is the ventralmost of the pair, the m. iliocostalis capitis origin appears to arise strictly from the C1 rib. Palpation of the ribs and incision into the fascia reveal the fascia’s continuity with the origin of m. iliocostalis capitis.

Insertion: In both birds and crocodilians m. r.c.l./m. il. cap. usually has a flat tendinous insertion along the ventral edge of the paroccipital processes ( Figs 5C , 6B ). In crocodilians the muscle is a mediolaterally broad band, but in most birds (e.g. Pelicanus occidentalis ) the belly of m. rectus capitis lateralis is dorsoventrally deep where it runs lateral to m. rectus capitis dorsalis. The insertion of this muscle in Varanus dumerilii is onto the basioccipital, ventromedial to the position of insertion in extant archosaurs.

Action/function: In extant archosaurs this muscle is well positioned to impose lateral flexion of the head versus the neck. EMG of crocodilians indicates that it is also active during head rotation, and during elevation, when it may serve a damping function for head dorsiflexors ( Cleuren & De Vree, 2000).

M. rectus capitis ventralis (m. r.c.v.) ( Vanden Berge & Zweers, 1993; Cong et al., 1998). ( Aves, Crododylia)

M. longus capitis ( Cong et al., 1998). ( Crocodylia ) M. flexor colli ( Vanden Berge & Zweers, 1993). ( Aves )

These muscles are associated with the processus spinosus ventralis and ventral surfaces of the cervical centra.

Origins: In birds, lateral and medial parts of m. rectus capitis ventralis (m. r.c.v.; Fig. 12 ) often originate from the ventral surface of processus spinosus ventralis (hypopophysis) of each vertebra from C2 to C5 or C6 (see Fig. 18). These slips coalesce to form a large muscle in many birds; it is especially large relative to the size of the head in Falco columbarius .

In Caiman crocodylus and Alligator misssippiensis the origin of m. rectus capitis ventralis is restricted to the ventrolateral surfaces of the centra of C1 and C2 (Fig. 13E). The origins of m. longus capitis are from the lateral surfaces of the processus spinosus ventralis of C3–C7, forming a large, anteriorly coursing belly.

M. flexor colli of birds typically originates aponeurotically from the ventrolateral surfaces of posterior vertebrae, associated with processus caroticus, when present, or with the processus spinosus ventralis.

Insertions: In the dissected birds the insertion of m. r.c. v. was typically anteroventral to that of m. longissimus capitis profundus, onto the basitemporal plate ( Fig. 5C ). In the crocodilians the insertion of m. r.c.v was onto the posteroventral surface of the basioccipital tuberosities ( Fig. 6B ), ventral to the insertion of m. longissimus capitis profundus. The insertion of m. longus capitis appeared to be continuous dorsally with that of m. r.c.v. ( Fig. 6B ) The insertions of m. flexor colli of most dissected birds were onto the posterior surfaces of processus spinosus ventralis on vertebrae anterior the origin.

M. r.c.v. of Varanus dumerilii is similar to that of crocodilians. M. flexor colli is similar to that of birds, but consists exclusively of uniarticular bellies running from the lateral surface of the processus spinosus ventralis of a posterior vertebra to the posterior surface of the preceding processus spinosus ventralis.

Action/function: The insertion of m. r.c.v. is ventral to the occipital condyle in crocodilians and anteroventral in birds, which indicates that the muscle ventroflexes the head relative to the vertebral column. The insertion of m. longus capitis of crocodilians is closer to the occiput than that of m. r.c.v., and, as with several such muscles in crocodilians ( Cleuren & De Vree, 2000), probably acts to stabilize the craniocervical joint during vigorous feeding behaviour.

Slips of m. flexor colli of birds (and Varanus dumerilii ) are well positioned to ventroflex intervertebral cervical joints that they cross.

M. longus colli ventralis (m. l.c.v.) ( Vanden Berge & Zweers, 1993). ( Aves)

M. iliocostalis cervicis (m. il. cerv.) ( Seidel, 1978), m. longus colli ( Cong et al., 1998). ( Crocodylia )

As with the major neck dorsiflexor ( m. longus colli dorsalis/m. transversospinalis lateralis), m. longus colli ventralis/m. iliocostalis cervicis is greatly elaborated in birds relative to the condition in crocodilians. Its origins and insertions are considered separately for the extant taxa.

Origins: M. longus colli ventralis is divided in birds into multiple sets of interconnected origins, intervening tendons, bellies and insertions, each spanning several vertebrae (Fig. 13). The posteriormost extent of a given system is usually a fleshy origin from the processus spinosus ventralis or sublateral process of a vertebra (Fig. 13B). (The hypopophyses are usually large and medially placed fusions of processes caroticales, while the sublateral processes are smaller and paired.) More than one slip complex of m. l.c. v. can arise from a given origin, and more anteriorly originating, smaller bellies can insert on intervening tendons of a given slip. Posteriorly slips can originate from the body of the centrum. In Leptoptilos crumeniferus large fusiform bellies arise from the ventral surfaces of mid and anterior thoracic

› Figure 13. A, the posteriormost subdivision of m. longus colli ventralis of Leptoptilos crumeniferus , depitcted in ventrolateral view. The outlined bellies originate deep in the thoracic region, and insert on light-coloured tendons to the posterior cervical ribs. The inset shows the morphology without highlighting. B, C, anteroventral views of the anterior vertebrae of Asio flammeus , depicting origins (B) and insertions (C), in dark shading, of m. longus colli ventralis. In B arrows represent schematic action of multiple slips of m. l.c. v. converging on an anterior insertion. D, ventral view of insertions (light shading) of m. iliocostalis cervicis onto the cervical ribs of Caiman crocodylus, with arrows representing schematic ventroflexive action. E, cervical vertebrae and ribs of Caiman crocodylus in oblique ventral view, depicting origins (dark shading) of m. rectus capitis ventralis and m. longus capitis, and m. iliocostalis cervicis (lighter shading), from the ventral centra and ventral spinous processes.

vertebrae of the notarium, deep in the thoracic region (Fig. 13A).

In crocodilians, parts of the m. iliocostalis cervicis/ m. longus colli (m. il. cerv.) system originate from the hypopophyses and ventral surfaces of the centra of the anterior thoracic and posterior cervical vertebrae (Fig. 13D, E). Dorsal origins occur on the capitula of the ribs; Seidel (1978) reported origins from the anterior portion of the myoseptum associated with each rib.

Insertions: Slips of m. l.c. v. insert by long tendons, 3–10 vertebrae anterior to their origin, with slips situated anteriorly crossing fewer joints than more posterior slips. These tendons run anterolaterally to insert on the cervical ribs (Fig. 13C) if these are well developed, or on the postlateral processes. Origins and insertions are difficult to tease apart in smaller birds.

In crocodilians, m. il.cerv. inserts ventrally onto the posterior processes of the cervical ribs (Fig. 13D), and dorsally by short slips onto the myosepta of ribs just anterior to their origin. The anteriormost insertion is by a white aponeurosis onto the rib of C1.

Action/function: The multiple slips of m. l.c.v. of birds potentially allow complex intervertebral ventroflexion. Anterior and posterior portions of the system are active during both approach and retraction phases of pecking and filter feeding, acting to ventroflex appropriate portions of the neck relative to posterior vertebrae, but also to damp the actions of dorsiflexive muscles ( van der Leeuw et al., 2001). In ducks the anterior and posterior slips fire asynchronously during approach, assisting with the complex rolling neck kinematics of feeding ( van der Leeuw et al., 2001).

Because insertions of m. il. cerv. in crocodilians lie lateral to the midline of the neck, kinematically the muscle complex appears capable of neck lateral flexion versus the trunk by unilateral contraction. The insertions are ventral to the intervertebral articulations, indicating the potential for neck ventroflexion as well. EMG of m. iliocostalis cervicis of crocodilians does indicate intense muscle activity during lateral flexion of the neck ( Cleuren & De Vree, 2000). However, the muscles are not active during ventroflexion, and instead show damping and stabilizing activity during dorsiflexion ( Cleuren & De Vree, 2000).

Figures

Figure 4. Comparison of major sites of muscle attachment on the necks of tyrannosaurids versus crocodilians and birds. A, cervical series of Caiman crocodylus (above; C1–C9) and Tyrannosaurus rex (below; C1–C10), depicting similarities of posterior transverse process morpohology. B, cervical series of Asio flamaeus (above) and Tyrannosaurus rex (below), depicting morphological similarities of epipophysis and the C2 neural spine. In all three groups the anterior transverse processes are smaller than their posterior counterparts (to show this clearly the C2 cerivical rib of T. rex is not pictured). Cervical rib morphology differs markedly among these archosaurs. The specimens are scaled to similar lengths from C1 to C9. The Tyrannosaurus rex is a composite reconstruction of C1 from Osborn (1905), BHI 3033 (C2) and AMNH 5027 (the remaining bones).

Figure 5. Attachments of muscles inserting on the occiput of birds. A, posterior cervical vertebrae of Strutio camelus, showing osteological origin of posterior belly of m. biventer cervicis. B, anterior cervical vertebrae of Haliaeetus leucocephalus, with origins of m. complexus, m. splenius capitis and m. rectus capitis dorsalis (outlined). M. complexus originates from the epipophyses dorsally (as in Haliaeetus leucocephalus), and sometimes the lateral tubercles ventrally. For adjoining origins of m. complexus and m. rectus capitis dorsalis from the lateral tubercles, the latter is the anterior of each pair. C, occiput of Struthio camelus, depicting all insertions. In Struthio camelus and many other birds m. splenius capitis lateralis inserts laterally onto the occiput, but in other birds part of m. complexus inserts here.

Figure 6. Neck muscle origins and insertions in crocodilians. A, muscle attachments on C1–C9 of Caiman crocodylus. B, muscle insertions on the occiput of Caiman crocodylus. m. trans. cap., m. transversospinalis capitis; m. epi.-cap. lat., m. epstropheo-capitis lateralis; m. epi.-cap. med., m. epstropheo-capitis medialis; m. sp.cap. post., m. spinocapitis posticus; m. trans. cerv., m. transversospinalis cervicis; m. long. cerv., m. longissimus cervicis (m. articulares/m. tendinoarticulares); m. long. cap., m. longus capitis; m. long. cap. sup., m. longissimus capitis superficialis; m. long. cap. prof., m. longissimus capitis profundus; m. il. cap., m. iliocostalis capitis; m. il. cerv., m. iliocostalis cervicis.

Figure 8. A, lateral view of m. longus colli dorsalis pars cranialis (m. l.c.d. cranialis), m. longus colli dorsalis pars caudalis (m. l.c.d. caudalis) and mm. intertransversarii (mm. intertrans.) of Cygnus columbianus. Note posterior slips contributing to m. l.c.d. cranialis, ventrally inserting heads of m. l.c.d. caudalis and multiple tendinous divisions of all mm. intertrans. B, left m. transversospinalis cervicis (m. trans. cerv., outlined in grey) of Caiman crocodylus, inserts by a white tendon onto C1. M. spinocapitis posticus (m. sp. cap. post.) and m. longissimus capitis superficialis (m. long. cap. sup., with part of surrounding fascia left on) are also outlined in grey. Superficial muscles have been removed.

Figure 9. A, insertions of (dark grey) m. longus colli dorsalis pars cranialis onto anterior cervical epipophyses of Haliaeetus leucocephalus. B, schematic origin (light grey) of m. longus colli dorsalis pars cranialis, from cervicodorsal region of Struthio camelus. C, schematic origins (dark grey) of m. longus colli dorsalis pars cranialis from epipophyses (processes dorsales) of posterior cervicals in Struthio camelus. Slips from these origins coalasce with the main belly of the muscle, as demarcated by the light-shaded lines. The main belly of the muscle continues dorsally. D, schematic origin and insertions of m. longus colli dorsalis pars caudalis. This muscle subsystem originates from the cervicodorsal region and sends multiple bellies to insert on posterior cervical epipophyses. E, origins of m. longissimus cervicis/m interarticulares of Caiman crocodylus. The gradient-filled slips represent association of origins with the fascia surrounding the muscles. F, anteriormost insertions (dark grey) of m. longissimus cervicis/m. interarticulares, and m. transversospinalis cervicis, of Caiman crocodylus.

Figure 10. A, several muscles of Pelicanus occidentalis, disseted in lateral view. Abbreviations are as in the main text. Several slips of m. rectus capitis dorsalis (m. r.c.d.) converge ventrally, towards tendinous insertions on the basioccipital tuberosities. M. complexus has an unusual lateral, tendinous insertion. B, posterolateral view of m. longissimus capitis superficialis (outlined in dark grey) of Alligator mississippiensis. The posterior origin and the insertion are tendinous. M. iliocostallis capitis (m. il. cap.) is depicted, and m. constrictor colli has not been dissected away. The neck is slightly dorsiflexed in this view.

Figure 11. A, origins (dark shapes) and insertions (lighter outlined shapes) of mm. intertransversarii aponeuroses on posterior cervical vertebrae of Struthio camelus. Origins are from anterior faces of lateral tubercles, and insertions are onto posterior projections of the lateral tubercles. Arrows represent lines of action whereby insertions are drawn towards the origins to effect intervertebral lateroflexion. B, origins (dark) and insertions (lighter) of mm. inclusii on posterior cervical vertebrae of Struthio camelus. Origins are from anterior faces of the costal processes, and insertions are onto the lateral and dorsolateral tubercles. Arrows represent lines of action whereby insertions are drawn towards the origins. C, origins (dark-filled shapes) and insertions (light-filled shapes) of lateral portions of mm. intertransversarii in Caiman crocodylus. Arrows represent lines of action from origin to insertion, by which the muscles would lateroflex the anterior vertebra of each pair relative to the posterior one.

Figure 12. A, origins of m. rectus capitis lateralis (m. r.c.l.) and rectus capitis ventralis (m. r.c.v.) of Corvus brachyrhynchos, from C2 prosessus ventralis. B, all origins of m. r.c.v. from anterior cervicals of another specimen of Corvus brachyrhynchos, and its m. rectus capitis lateralis origin from C2. Both images are ventrolateral views. C, ventrolateral view of m. rectus capitis ventralis (with light outline) of Falco columbarius.