228 REPORT— 1873. 



in the interorbital space, and receding from each other over the parietal 

 tract. Sometimes they are seen to converge once more towards the anterior 

 or external nares, completing thus the figure of a lyre, wliich they have been 

 thought to resemble. They become deeper and more defined with age. 



In Trematosaunis, Bncmeister* distinguishes frontal, malar, and maxillary 

 canals (" Stirn-, Backen-, und Mundrand-Furchen ''). The frontal canals are 

 first conspicuous between the anterior nasal apertures, running parallel to 

 each other at this point. They pass in diverging curves backwards across 

 the snout, are approximated towards the orbits, immediately behind which 

 they diverge again, and then terminate. The malar canals are somewhat 

 broader. They pass forwards from the aperture of the ear to the centre of 

 the postorbital, curve downwards to near the angle of the mouth, where they 

 touch the maxillary canals, and then take a nearly straight course across 

 the jugal and supratemporal to the posterior margin of the skull. The 

 maxillary canals are faintly marked at tlieir origin near the tip of the 

 snout, but become gradually broader and deeper. They rise a little upon 

 the side of the skull halfway between the nasal apertures and the orbits, 

 but are contiguous to the edge of the mouth throughout the rest of their 

 course. They disappear gradually near the angle of the mouth. The mucous 

 canals of Mastodonsaurns are very similar, but the lyra is more dilated and 

 more regularly oval. In Oonioglyptus-\ the facial canals are strongly angu- 

 lated, curving outwards and forwards from the interorbital space, and then 

 suddenly becoming parallel. 



In Archegosaurus the mucous canals are visible only in the large skulls. 

 They are distinct along the inner border of the orbit, passing thence for- 

 wards upon the prefrontal, and backwards upon the postfroutal and supra- 

 temporal. Burmcisters restoration J seems to exhibit the canals too pro- 

 minently upon the prcorbital part of the face. 



In Loxomma the canals pass in simple curves from the inner borders of 

 the orbits to the posterior external angles of the premaxillaries, and are 

 united in front by a slightly curved canal which runs along the free border 

 of the pi-emaxillaries above the alveolus. A short maxillary canal is pre- 

 sent in this genus. 



Tlie skulls of Crocodilia agree with those of the Labyrinthodonts in having 

 a pitted sculpture, though in the former order the pits and grooves are not 

 usually radiate. Mucous canals are not found in Crocodilia. Both kinds 

 of sculpture are, in all jirobalfility, related to the nutrition of the cutis. 



The crania] bones (witli the exception of the quadrate and parts of the 

 occipital segment in many Carboniferous Labyrinthodonts) are fully ossified, 

 and this from the time that the animal leaves the shell. As a rule, no inter- 

 spaces or fontanelles are visible at any age§, though examples oi Archego- 

 saurus of embryonic size, in which the skull was not more than one twentieth 

 of the length of the adult state, have been examined with reference to this 

 point. 



This mode of development of the skull is not confined to Labyrinthodonts. 

 In Crocodilia the same thing is observed. A recently hatched Crocodile pre- 

 sents no cranial interspaces or fontanelles. Not only are the sutures of the 

 Crocodilian skull closed before the end of embryonic life, but the frontals and 



* Trematosaiirns, p. 6. 



t Huxley, "Vertebrate Fossils from the Panchet Eocks," PaltEontologiea Indica, p. 5 

 t. vi. f. 1 (1865). 



J Archegosaums, p. 8. t. It. fig. 1. 



^ A membranous interspace, or " facial fontanelle," exists in Basyceps. 



