THE SKULL OF CHIMiERA. 133 



found in ' my specimens of Chimcera colliei arising from the 

 tough fibrous tissues that cover the ventral surface of the sym- 

 physis of the mandibles, and also from the external surface of the 

 cartilage a. Running latero-posteriorly in a curved line, this 

 ligament is joined first by a ligament coming from the median 

 line posterior to the cartilage a, and then by a ligament coming 

 from the ventral edge of the mandibular labial and to which 

 reference has just above been made. The ligament so formed 

 runs posteriorly across the postero-ventral edge of the mandibula, 

 in a slight groove in that edge, and then runs upward along the 

 internal surface first of the mandibula and then of the palate- 

 quadrate, and is inserted on a little cartilage which seems' to 

 correspond to the spiracular cartilage of Hubrecht's descriptions 

 of Chimera monstrosa, notwithstanding that it lies much farther 

 from the hind edge of the mandibula. This little cartilage is 

 probably a persisting remnant of a mandibular branchial ray 

 such as is frequently found in the Selachii and there currently 

 called a spiracular cartilage, but it cannot be the homologue of 

 the spiracular cartilage of the Batoidei, that cartilage being the 

 extrabranchial, or suprapharyngobranchial, of the mandibular 

 arch and being represented, in Chimcera, in the processus oticus 

 quadrati, as already stated. The ligament related to this little 

 cartilage may then represent either certain persisting fibrous 

 tissues of the mandibular arch, or be a ligament derived from 

 certain fibres of the primitive constrictor of the arch such as are 

 found in Astrape (Luther, 1909 a, p. 14), and to which I have 

 made reference in a work now in press on the homologies of 

 the muscles related to the visceral arches in the gnathostome 

 fishes (Allis, 1917 a). If this little cartilage be a persisting 

 remnant of a mandibular branchial ray, then the cartilage a 

 would also seem to be such a remnant. Luther (/. c. p. 46) 

 considers the cartilage a to be a chondrification of the membrane 

 in which it lies. 



3. Bostral Processes. 



The three rostral processes of the adults of all of the Chimaa- 

 roids are said by Garman (1904) to be attached to the chondro- 

 craninm by ligaments "in such a way as to admit of considerable 

 movement of their distal extremities up and down," the evident 

 inference being that Garman did not find, in any of these fishes, 

 the cartilage of these processes continuous with that of the chon- 

 drocranium. Hubrecht, however, shows all three of these 

 processes directly continuous with the cartilage of the chondro- 

 cvaninm, and he suggests that the median process may be the 

 homologue of the rostral process of the Selachii, and that 

 the lateral processes are probably represented, in the latter 

 fishes, by ligaments. Schauinsland (1903) refers to these pro- 

 cesses, in embryos of Callorhynchus, as " mit dem Schadel fest 

 verbundenen Knorpeln," and in his figures he shows all three of 

 them as outgrowths of the septal cartilage of his descriptions 



