OCR Text |
Show 1870.] AXIAL SKELETON OF THE URODELA. 275 caudal is in the same case ; but at the third, or sometimes the second caudal, this process suddenly reappears, greatly increased in size and generally united with its fellow of the opposite side, forming the first hypaxial arch. Such arches (figs. 1 & 15) are always present in the Fig. 15. Under view of anterior caudal vertebra? of Menobranchus (No. 582 A in College of Surgeons' Museum). c. Capitular process. Hy. Hypapophysis. caudal vertebras, except in Siren ; but there, though the caudal hypapophyses remain medianly disunited below, yet each is broad antero-posteriorly, as well as much vertically extended (fig. 8, Hy). The hypaxial arches are sometimes narrow from before backwards, though much elongated from above downwards; this is the case in Menopoma, Cryptobranchus, Menobranchus (fig. 10, Hy), and Proteus. In the three first-named genera especially they are produced obliquely backwards and downwards into long inferior spines, even exceeding in length the neural spinous processes above them, and are similarly bony cylinders unossified at their summits. Tn Axolotl and Amblystoma the hypaxial arches repeat the characters offered by the neural ones, inasmuch as each is provided with a pair of diverging sockets (fig. 6) apparently for the reception of two cartilaginous spines placed side by side. The posterior margin of these hypaxial or hypapophysial arches Fig. 16. Under view of 23rd, 24th, 25th, and 26th vertebra? of Amnkiuma. Hy. Hypapophysis. is often medianly notched like the corresponding margin of the epaxial or neural arches above. This correspondence is often further increased by the frequent development of a median longitudinal hypaxial crest, which, bifurcating at the notch, is continued forwards |