74 COMPARATIVE ANATOMY. 



the cartilaginous nasal capsule (compare the chapter on the auditory 

 organ, p. 199). 



With the exception of certain small regions on the dorsal side, 

 the skull of Anura consists of a complete cartilaginous box : in the 

 adult the bones are not so numerous as in Urodeles, and the frontal 

 and parietal of either side as a rule fuse together, thus giving rise 

 to a fronto-parietal. The maxillary bar grows backwards much 

 further than in Urodeles, and becomes connected with the suspen- 

 sorium by means of a small intermediate bone, the quadratojugal 

 (Fig. 59, Qjg}. For the relations of the bones bounding the mouth- 

 cavity, compare Fig. 59. 



With the exception of the lower jaw, the visceral skeleton 

 of Urodeles undergoes various modifications in the different types. 

 We may consider the ground-form, as present in the larva, to 

 consist of five pairs of bars. The anterior pair, or hyoid, consists 

 of two pieces (Fig. 60, A, HpH, KeH}, as do also the two first 

 branchial arches (Kcbr I, II, Eplr I, II}. The third and fourth 

 branchial arches are much smaller, and each is composed of a 

 single segment (Epbr III, IV}. All the above-named arches are 

 connected with their fellows the other side by means of a single 

 or double basal piece (Fig. 60, Bbr I and Bbr II}. At the close of 

 larval life, when the lungs come into use, the two hinder pairs of 

 arches disappear entirely, while the two anterior pairs undergo 

 changes as regards form and position, arid become more or less 

 strongly ossified (Fig. 60, B, C). In the genus Spelerpes, which 

 possesses a sling-like tongue, the lateral (dorsal) segment of the 

 first true gill-arch (epibranchial /) grows out into a long cartila- 

 ginous filament, which extends far back under the skin of the back 

 (Fig. 60, D). 



In the Anura there is a much greater reduction of the 

 branchial skeleton at the close of larval life than in Urodeles. In 

 the larva, the main skeletal part consists of superficial branchial 

 cartilages (extra-branchials), which form a continuous structure 

 comparable to the branchial basket-work of the Lamprey. A hyoid 

 and small rudiments of the four proper internal branchial arches are, 

 however, present behind the mandible. 



c. Reptilia. 



The relationship between the skulls of Reptiles and Birds is very 

 close, while both are widely separated from those of Amphibians 

 and Mammals. 



Excepting in the ethmoidal region, the whole chondrocranium 

 becomes almost obliterated by an extensive process of ossification. 



In Snakes, Amphisbaenians, and Crocodiles, the cranial cavity 

 extends forwards between the orbits as far as the ethmoidal region, 

 while in Lacertilia and Chelonia in which a fibro-cartilagmou? 



