Bos taurus, Linnaeus, 1758
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publication ID |
https://doi.org/ 10.1206/0003-0090-409.1.1 |
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persistent identifier |
https://treatment.plazi.org/id/03DE5621-FF8B-FFAB-FEF2-0FA2FB91FA78 |
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treatment provided by |
Carolina |
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scientific name |
Bos taurus |
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Figures 11–13 View FIGURE 11 View FIGURE 12 View FIGURE 13
There are several sources on Bos taurus basicranial anatomy ( Sisson, 1911; Getty, 1975; Schaller, 1992), but in some cases the terminology differs from that used in contemporary comparative anatomy and paleontology works ( Wible, 2003; Giannini et al., 2006; O’Leary et al., 2013) and many key structures are not labeled. The description here is based on two adult specimens: the bulla in situ is based on SBU-MAR 15 (fig. 12), and the bulla removed is based on SBU-MAR 14.
Several orbit landmarks are visible in figure 13. The optic foramen is round and the sphenorbital fissure is oval to teardrop shaped with a broad base inferiorly. The anterior opening of the pterygoid canal is a small slit at the base of the sphenorbital fissure; continuity with the posterior opening in the basipharyngeal canal is easily established with a probe. The foramen ovale is entirely contained within the alisphenoid directly anterior to the styliform process of the bulla.
Figure 12 View FIGURE 12 shows the posterior aspect of the basipharyngeal canal. The vomer extends far enough posteriorly that it is broadly visible as a significant component of the basipharyngeal canal roof. It terminates just anterior to the suture between the presphenoid and the basisphenoid. The pterygoid bones extend slightly distal to the posterior edge of the vomer and form important elements of the lateral wall of the basipharygneal canal and a small component of the orbital wall. The posterior edge of the basipharyngeal canal is a complex arrangement of the pterygoid, alisphenoid, and palatine. Anteriorly the palatine alone forms the ventral margin of the basipharygneal canal, but posteriorly the pterygoid also extends to contribute to the ventral edge of the canal. The alisphenoid is less extensive and is primarily limited to the lateral wall of the basipharyngeal canal. The hamulus is a very diminutive hook that projects posteriorly and laterally. There is no pterygoid fossa and no significant development of entopterygoid processes. At the posterior end of the pterygoid bones on the superior aspect of the basipharygneal canal is a small but distinct posterior opening of the pterygoid canal.
A craniopharyngeal canal lies between the anterior aspects of the tympanic processes in the midline (fig. 12). The tympanic processes are pronounced, roughened, and oval knobs. They are positioned anterior and medial to the bulla and have no contact with it. The anterior ends of the occipital condyles are distinctly separate anteriorly. They have pronounced flexion stops (fig. 12). The occipital condyles have distinct ventral and posterior surfaces separated by an occipital ridge. The paracondylar processes are short projections that are angled slightly toward the midline as they descend. They extend inferior to the ventral edges of the bulla and its styliform process. They terminate in a subtle knob. A large, single hypoglossal foramen is present on each side tucked superior to the flexion stops (there is one accessory hypoglossal foramen on the left side in SBU-MAR 15; fig. 12). This hole is wide, giving very direct passage between the foramen magnum and the outside of the skull. By contrast, the two condyloid canals, which are smaller than the hypoglossal foramina and posterolateral to them, have a longer route through the exoccipital between the foramen magnum and the outside of the skull.
The auditory bulla is relatively tightly held in place, particularly posteriorly and laterally (fig. 12). In the adult, the petrosal is almost fully obscured when the bulla is in situ. The bulla has a compressed, elongate ovoid shape that is oriented along an anteromedial to posterolateral axis. The bone is smooth textured and in places (e.g., posteromedially), so thin as to be transparent, revealing its internal cancellous structure through the bone. At the anteromedial extreme is a pronounced styliform process—a thin, elongate spike with a significant anteroventral projection that extends well inferior to the basisphenoid. The long styliform processes are widest at their bases where they contact the auditory bulla (figs. 11, 12). The ventral edge of the bulla bears a crest, the bullar ridge, which follows an anteromedial to posterolateral direction. The bullar ridge starts at the posterior aspect of the styliform process. As the ridge extends toward the posterolateral corner of the bulla, where it terminates posterior to the tympanohyal, it gives rise to several irregular knobs that are not bilaterally symmetrical in shape or number. The bulla forms a deep stylohyal fossa, where it wraps around the inferior end of the tympanohyal but does not completely enclose it posterolaterally. The infe- rior end of the tympanohyal is slightly flattened and does not project beyond the borders of the stylohyal fossa. A conspicuous semicircular crest on the bulla marks the anterior and anterolateral edges of the stylohyal fossa.
A distinct sulcus marked by sharp edges runs along the alisphenoid between the anterior bulla and the posterior and lateral margins of the basipharyngeal canal terminating at the posterior opening of the pterygoid canal. At the anteromedial edge of the bulla the carotid incisure is vis- ible with the bulla in place. The anterior carotid foramen is tucked deeply into the anterior aspect of the bulla and is not visible with the bulla in situ. The posterior carotid foramen is also not visible with the bulla in situ and this entry point into the middle ear is marked only by an inconspicuous groove on the bulla itself.
The stylomastoid foramen is a distinct circular opening just lateral to the posterior part of the exposed tympanohyal (fig. 12). The other three borders of the foramen are the exoccipital, the mastoid region of the petrosal, and the external acoustic meatus (less clear in fig. 13, where sutures are obliterated). There is a furrow leading out of the foramen and running along the squamosal posterior to the external acoustic meatus. The external acoustic meatus is longer mediolaterally than is the bulla. A narrow ridge of bone runs the entire length of the external acoustic meatus from the porus acusticus externus to the tympanohyal. This bony ridge projects ventrally from the bulla for several centimeters. The porus acusticus externus is inset medially relative to the lateral edge of the skull. The external acoustic meatus has a number of minute, irregularly positioned small holes (fig. 12). The external acoustic meatus is also fused posteriorly to the mastoid region of the petrosal, to the posttympanic process of the squamosal laterally and posteriorly, and to other parts of the squamosal anteriorly. The sutures are obliterated. At the porus acusticus externus it is apparent that the ectotympanic part of the external acoustic meatus forms a completely circular tube that lies within (and is fused to) a depression on the squamosal. However, due to fusion, this tube cannot easily be removed intact (fig. 11). The bulla is in extensive contact with the petrosal during life and also contacts the basisphenoid/basioccipital area medially. Not shown in the illustrations is the contact between the bulla and the alisphenoid anterolaterally. The internal aspect of the bulla contains numerous chambers of cancellous bone.
With the bulla removed, the large piriform fenestra is exposed between the anterolateral petrosal and the alisphenoid/squamosal (fig. 13). The piriform fenestra is fully contiguous with the carotid foramen, which forms a notch in the midline near the junction between the basisphenoid and basioccipital (suture is obliterated). The carotid incisure is fully confluent with the middle lacerate foramen and the basicapsular fissure. Posterior to this area the petrosal abuts the basioccipital and may be fused. This junction separates the jugular foramen from the basicapsular fissure, and each of those openings leaves small notches in the basisphenoid/basioccipital. The jugular foramen is an elongate oval.
The glenoid fossa is situated on the posterior aspect of the squamosal contribution to the zygomatic arch (fig. 12). The fossa is mediolaterally elongate, with a convex preglenoid process anteriorly and concave area posterolaterally. In the isolated bulla, grooves for the anterior and posterior carotid foramina are inconspicuous. A medial glenoid pit is present. Posterior to the glenoid fossa is a small postglenoid process situated on the medial aspect of the joint. Posterior to the postglenoid process lies the postglenoid foramen adjacent to a medially positioned accessory postglenoid foramen of smaller size. In SBU-MAR 15 these two openings are also joined via a canal posterior to the postglenoid foramen; in SBU-MAR 14, this canal is absent. The larger of the two foramina is situated more medially and directly behind the postglenoid process (this process is shown in situ in fig. 12 and removed to show foramina in fig. 13). Medial to the medial glenoid pit is a scroll of bone (part of the alisphenoid) that lies just anterior to the bulla but does not touch it.
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