325 



Ayers and Jackson's descriptions. However this may be, either the 

 whole or a part of the hypophysial plate of Bdellostoma would seem 

 to be the homologue of the whole or a part of the floor of the eye- 

 muscle canal of Amia. The lateral edge of the anterior half of this 

 plate is connected by membrane with the mesial edge of the so-called 

 palatine, and that membrane is pierced by the ramus palatinus posterior 

 trigemini after that nerve has passed below the palatine. The mem- 

 brane thus seems to represent a part of the side wall of the eye- 

 muscle canal of Amia, and the so-called palatine cartilage a part of 

 the side wall of the skull. The so-called palatine is in fact, to all 

 appearance, simply an anterior continuation of the trabecula, and as 

 such I consider it. Parker considered it as half palatine and half 

 trabecula. 



Posterior to the anterior horn, tr, of Ayers and Jackson's de- 

 scriptions of the trabecula, the membrane that connects the anterior 

 half of the hypophysial plate with the palatine, extends but a short 

 distance, there lying between the two heads of the velo-quadratus 

 muscle. Another membrane, however, here begins. It arises from the 

 lateral edge of the subocular part of the so-called pterygo-quadrate, 

 and runs downward and mesially around the velar muscles toward the 

 lateral edge of the posterior portion of the hypophysial plate. It did 

 not seem, in my sections, to actually reach that plate, and it becomes 

 thin and delicate toward its ventro-mesial edge. The several branches 

 of the ramus maxillo-mandibularis, as they issue from beneath the 

 subocular arch, pierce the dorsal edge of this membrane. The fact 

 that this membrane, and the posterior portion of the anterior one, 

 partly enclose the velar muscles is interesting because of Hatschek's 

 (11) statement, confirmed by v. Kupffer (15, p. 56), that, in Ammo- 

 coetes, the obliquus superior muscle is developed from an anterior 

 prolongation of these very muscles; a muscle, possibly related to the 

 eye-muscles, thus, in these fishes, where the eye is presumably primi- 

 tive, having relations to a subcranial canal. The velar muscles, in 

 hoth Ammocoetes and Bdellostoma, are innervated by a special branch 

 of the maxillo-mandibularis trigemini, an innervation that might be 

 interpreted as favourable either to the assumption that the nervus 

 trochlearis is a dorsal nerve, or that it is a ventral one. 



In Lepidosiren, Bridge (6) says that, with the exception of the 

 ophthalmicus trigemini, the primary branches of the trigeminus and 

 facialis, "may almost be said to leave the cranial cavity by a single 

 large foramen leading into a lateral diverticulum of the cavity, situated 

 at the junction of the trabecular and periotic cartilages". He calls 



