292 report— 1846. 



only the nerve-trunks to be protected by the nasal neurapophyses. These 

 are, therefore, more approximated, and the anterior termination of the neural 

 canal is much contracted ; and, in the tailless batrachia, the nasal neur- 

 apophyses coalesce together. 



We recognise in that element (20) of the fourth or foremost inverted arch 

 of the crocodile's skull, which is in connection with the body (vomer, 13) and 

 descending plates of the neurapophyses (prefrontals, 14) of the nasal vertebra, 

 the proximal or pleurapophysial element of such arch; and the same repe- 

 tition of the characteristic connections of the bone, 20, which enabled Cuvier 

 and GeofFroy to recognise its special homology with the palatine bone in the 

 fish, establishes its claim to be equally regarded in the crocodile as the pleur- 

 apophysis of its vertebral segment ; although it now affords but a partial at- 

 tachment to the bone 21, which forms the next element of the inverted arch. 

 This bone, the hcemapophysis, has undergone a striking change in its propor- 

 tions by development both in length and breadth: it is connected not oniy with 

 no. 20 behind and with no. 22 before, but with the elongated spine, no. 15, of its 

 own vertebra, and with the lacrymals, 73, above ; with its fellow of the opposite 

 side below, and with a well-developed proximal element, no. 26, of a strong 

 diverging appendage behind. The hcemal spine, no. 22, is divided, and the 

 arch is completed by the symphysial junction of the two halves at H iv. The 

 nasal aperture or entry to the air-passages forms the span or area of the 

 much-modified inverted arch constituting the upper jaw of the crocodile. 

 The two proximal elements of the arch, nos. 20 and 21, continue to send 

 outwards and backwards exogenous diverging processes ; but they consti- 

 tute a smaller proportion of the bones than in fishes, and both processes di- 

 rectly support distinct bones representing the diverging appendage of the 

 arch, and serving to fix and attach it to the succeeding arch. The pleurapo- 

 physial appendage (pterygoid, 24) soon coalesces, however, with its fellow 

 and with the centrum of its own vertebra (vomer, 13), and then expands to 

 unite by a broad sutural surface with the coalesced centrums of the frontal 

 and parietal vertebra? (9 and 5). A second osseous piece (ectopterygoid, 

 24') diverges from the pleurapophysis external to the preceding and attaches 

 it to the haemapophysis, to the haemapophysial appendage, and to the par- 

 apophysis of the frontal vertebra. The strong diverging ray from the haem- 

 apophysis is teleologically subdivided into nos. 26 (malar) and 27 (squamosal), 

 and firmly attaches the maxillary arch to the pleurapophysis (2s) of the man- 

 dibular one. 



In the chelonian reptiles the modifications of the nasal segment of the 

 skull adhere pretty closely to the type of those in the crocodile ; the centrum 

 is more independent and better developed, but the divisions of the neural 

 spine have coalesced with their neurapophyses : the diverging appendages, 

 26 and 27, are usually developed into broad and flat bones. In many lizards 

 we find the nasal centrum divided but the neural spine single : the hajmal 

 spine is, also, single, as a general rule, and sends upwards and backwards a 

 process to join the neural spine, divide the area of the haemal canal, and 

 terminate the vertebral series anteriorly. The haemapophysial diverging ap- 

 pendage commonly resumes its long and slender ray-like proportions, and joins 

 the parapophyses of both frontal and parietal vertebrae as well as the prox- 

 imal end of the pleurapophysis of the mandibular arch. In serpents both 

 divisions of this appendage are absent (indicating the inferior character of 

 the bones 2s and 27 in general homology), but the two parts of the pleurapo- 

 physial appendage, 24 and 24', are retained and serve as levers in the move- 

 ments of the maxillary arch. The spine of that hasmal arch is single, and 

 commonly united only by lax and elastic ligaments with the haern apophyses, 



