— 186 — 



and backward in a deep groove that lies on the orbital surface of the proötic and that leads into a 

 large trigemino-facialis Chamber. This groove, in Lepidosteus, transmits the ramus palatinus 

 facialis as well as the external carotid artery, the nerve traversing the foramen in the proötic with 

 the artery, and entering the carotid canal. This foramen in the proötic of Lepidosteus is accordingly 

 the homologue of the palatinus and external carotid foramina of Amia, coalesced into a single opening. 

 It has closely the position of the palatinus foramen of Amia, and neither it nor the carotid foramen 

 are shown by Parker in any of his figures. 



In sections of embryos, a delicate pharyngeal branch of the glossopharyngeus is found accom- 

 panying the common carotid artery, and although it could not be traced as far as the carotid foramen, 

 it doubtless traverses that foramen, with the artery, as in Amia. 



The internal carotid artery, having separated from the external carotid immediately beneath 

 the palatinus foramen, runs forward in a canal between the cartilage of the basis cranii and the under- 

 lying parasphenoid, lying in a slight groove on the dorsal surface of the latter bone. It is accom- 

 panied, in this canal, by the ramus palatinus facialis and probably also by the delicate branch of the 

 glossopharyngeus just above described. Having arrived near the anterior edge of the ascending 

 process of the parasphenoid, and there lying anterior to the pituitary fossa, the internal carotid 

 receives the efferent pseudobranchial artery. It then, in all my embryos, immediately separates 

 into two parts. In the smaller embryos, these two parts both turn upward and traverse the inter- 

 trabecular space, while in the older embryos, they perforate the overlying cartilage and so enter 

 the cranial cavity, one part traversing a large foramen and the other traversing a small and imper- 

 fectly enclosed branch canal which leads from that foramen. The larger one of these two branches 

 gives off several intracranial branches and then leaves the cranial cavity with the nervus opticus. 

 The smaller branch also issues with the opticus, but it gives off no perceptible branches during its 

 intracranial course, and it may perhaps be reminiscent of the otherwise whoUy wanting anterior 

 continuation of the eiferent pseudobranchial artery. Shortly before the anastomosis with the efferent 

 pseudobranchial artery, the internal carotid gives ofE a small brauch which runs forward, accompanying 

 the palatinus facialis, in an anterior Prolongation of the canal between the parasphenoid and the 

 overlying cartilage of the base of the skull. This latter artery and the two carotids are all three briefly 

 mentioned by Wright ('85) in his description of the arterial circulation in embryos of Lepidosteus, 

 but their foramina and their courses relative to the craniura are not well or sufficiently given by him. 



In the adult, the trabeculae of opposite sides have fused with each other in the middle 

 line, and the internal carotids traverse foramina in the basis cranii, these foramina corresponding to 

 the internal carotid canals of my descriptions of Amia ('97). Slightly anterior to these canals there is 

 a shallow transverse groove across the dorsal surface of the fused trabeculae, this groove corresponding 

 exactly, in position, to the canalis transversus of my descriptions of Amia, and being quite undoubt- 

 edly the homologue of that canal. The groove is, however, not the homologue of the canalis trans- 

 versus of selachians, as I have pointed out in a later work ('Ol), and the selection of the name, in my 

 descriptions of Amia, was unfortunate. The groove, in Lepidosteus, forms the anterior boundary 

 of a slightly raised portion of the cartilage of the basis cranii, which extends backward to the anterior 

 edge of the pituitary fossa and is the homologue of the much more pronounced transverse prepituitary 

 bolster of Amia. 



The pseudobranchial artery, in Amia, does not itself fuse with the internal carotid, a smaU 

 communicating branch, only, which perforates a lateral projection of the basis cranii, uniting the 



