59 



■have fused with the neurocranium ; the processus oticus fusing with 

 the otic capsule and the processus basalis with the parachordal cartilage. 

 In Ceratodus it is the processus basalis that first fuses with the neuro- 

 cranium, then the processus oticus, and last of all the processus as- 

 cendens. The pharyngeal tissues that I have assumed, in an earlier 

 work (1914b), to be related to the mandibular arch must therefore 

 chondrify, in Ceratodus, before the premandibular tissues, while in 

 urodeles the order of chondrification is reversed. 



Of the Anura, Rana fusca is the only one in which I find the 

 relations of the nerves, arteries and veins to the chondrocranium 

 sufficiently well described for the purposes of this discussion. In 

 early larvae of this anuran (Gaupp, 1893), the lateral wall of the 

 trigemino-facialis chamber is represented by the processus ascendens 

 and oticus quadrati, the mesial wall and the floor of the chamber not 

 being found. After the metamorphosis the pre-trigeminus portion of 

 the lateral wall, represented by the processus ascendens, has been 

 resorbed, leaving only the post-trigeminus portion of that wall (pro- 

 cessus oticus) ; but a mesial wall, perforated by the roots of the tri- 

 geminus and facialis nerves, has now been developed, as has also a 

 floor, this floor being represented by the processus basalis. This is 

 all evident from the strictly similar relations of the nerves, arteries 

 and veins to the several processes in this anuran and in Salamandra 

 and Ceratodus. In the earliest larvae of Rana examined by Gaupp 

 the arteria carotis interna, running upward, is said to first give off a 

 palatine branch (arteria palatina), and then to enter the cranial cavity 

 through the foramen caroticum. There it immediately gives off a small 

 branch and then separates into two parts, the arteriae ophthalmica 

 and carotis cerebralis. The small branch first given off runs forward 

 a short distance in the cranial cavity and then issues from that cavity 

 through the foramen cranio-palatiuum, after which it continues its 

 forward course ventral to the chondrocranium. In later stages this 

 small branch is said to wholly abort, its foramen of exit, however, 

 persisting for a time. This all seems to quite certainly indicate that 

 this small branch is the primary anterior portion of the lateral dorsal 

 aorta and hence the homologue of the arteria orbito-nasalis of teleosts 

 (Allis, 1914 c). 



.Of Reptiles, it will be sufficient to consider Lacerta and Crocodilus. 



In embryos of Lacerta (Gaupp, 1900), the pre-trigeminus (pre- 

 mandibular) portion of the lateral wall of the trigemino-facialis chamber 



