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MacPhee, Ross D. E., Gaillard, Charlène, Forasiepi, Analía M. & Sulser, R. Benjamin, 2023, Transverse Canal Foramen And Pericarotid Venous Network In Metatheria And Other Mammals, Bulletin of the American Museum of Natural History 2023 (462), pp. 1-125 : 32-33

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CAENOLESTES ( CAENOLESTIDAE ) (figs. 13, 14). Despite much early interest in the morphology and relationships of Caenolestes (e.g., Dederer, 1909; Gregory, 1910; Broom, 1911), a thorough investigation of its mesocranial anatomy has never been undertaken. Osgood’s (1921) monograph provides some information on the carotid and transverse canal foramina, but he did not investigate vascular contents or intracranial connections. Herrick’s (1921) complementary study of the external morphology of the brain in Caenolestes provides a few helpful observations, such as the size and position of the hypophysis.

As whole specimens of shrew opossums were not available for this study, our analysis is based on a scanned skull ( Caenolestes sp. IANIGLA uncataloged) supplemented by specimens in the AMNH Mammalogy collection. Within the endocranium, the eminences of the canals for the rostral branches of the TCVs and the rostral TBS form low but very distinct mounds on the endocranial surface of the basisphenoid (figs. 13D; 14A– C). The mesocranium of Caenolestes appears to differ little from that of non- Didelphis didelphids. In junction pattern Caenolestes seems more similar to Monodelphis (fig. 12A) than to Dromiciops (fig. 15D, 17A–D), in part because the TBS does not surround the RBTC canals.

In figure 13D, the CBF can be seen at the rostral end of the carotid groove; it opens into a short sulcus that communicates with the endocranial carotid foramen and thus the CS/ICV (fig. 12D). In the scanned specimen the CBF is separate from the carotid canal, but in some of the other material examined (e.g., Caenolestes convelatus AMNH M-64457) these apertures appear to be continuous. Hypophyseal canaliculi on the periphery of the hypophyseal fossa presumably transmitted small veins to/from the CS (figs. 13D; 14C: feature 1). Similar apertures are lacking in Didelphis (fig. 2C).

Sánchez-Villagra and Wible (2002: 28) considered the intramural character state to be absent in Caenolestes because a hair probe simply went straight into the endocranium. This illustrates the limits of the probe approach: although the rostral canals are clearly present, probing failed to find them because of the sharp turns that would have been required to manipulate the probe in the proper direction.

Other features of interest are the large apertures situated along the flanks of the rostral TBS well in advance of the junction (fig. 13D: asterisks). These are positioned too rostrally to be morphologically part of the transverse canal apparatus, but they might be related to the ophthalmic veins in some way. Similar foramina were also encountered in dry specimens of C. fulginosus (e.g., AMNH-M 64455).

The basicapsular fenestra is widely open for most of the length of the petrosal-basioccipital interface, but foramina for the EVPS and IJV are distinct and separate. The paired tubes that pass through the lateral margins of the basioccipital (fig. 14E–G: asterisks) communicate with the sulci for the VPS and are doubtless vascular, but their significance is otherwise uncertain. Terminating in the condylohypoglossal foramina, these accessory canals diminish rather than increase in size caudally, indicating that they receive few or no additional vascular inputs.