114 E. EAMSAY WRIGHT ON THE SKULL AND AUDITOEY 



parts of the labyrinth. It is entirely behind the anterior branch of the auditory nerve, 

 which is, as usual, chiefly distributed to the macula recessi'is utriculi, but shows the rela- 

 tion of the saccular and lagenar branches of that nerve in their backward course. The 

 relationship of the trigeminal lobe of the medulla oblongata to the utriculus is somewhat 

 peculiar. On account of the large size of the former it projects backward laterad of the 

 utriculus, which, accordingly, does not lie close against the skull, as is usual in the 

 Teleostei. Worthy of note is the relatiA^e size of the osseous and external semicircular 

 canal in the pterotic, and the neuromastic canal in the same bone. This section falls 

 behind the parietal part of the supraoccipital, and, consequently, through the grooved 

 spine, and that part which serves for the attachment of the dorsal musculature, and for the 

 shelter of the anterior part of the posterior semicircular canal. 



Fig. 10 represents a section immediately behind the foramen for the glossopharyngeus ; 

 the position of that foramen being indicated by an arrow on the left side of the figure. 

 The exoccipital is pierced in this plane by a small branch of the glossopharyngeus, which 

 accompanies the ramus ampullœ posterioris, and is undoubtedly a dorsal branch, as it is 

 distributed to the neiiromast in the pterotic. I found no dorsal branch of the glosso- 

 pharyngeus in Amiurus, and the position of escape and course of this is sufficiently 

 remarkable. 



In the skull in this region we find cartilage persisting between all of the bones, viz., 

 the supraoccipital, exoccipital, epiotic, pterotic, and basioccipital. The form and relations 

 of the exoccipital can be better studied from this and the following sections than from 

 the figirres of the skull Applied against the pterotic is the most anterior part of the 

 supraclavicle, the architecture of the osseous trabeculte of which exhibits a striking con- 

 trast to the pterotic with which it is fused. The neuromastic canal now lies against the 

 pterotic cartilage, and is protected on the outside by the supraclavicle. 



Certain interesting points are observable in this section with regard to the auditory 

 labyrinth. The transverse duct connecting the saeculi of both sides is met, and the wall 

 of the duct is attached to a crest on the basioccipital, as is also the case in Amiurus 

 (Fig. 8, PL VI, loQ cU.), from which it will also be seen that the relations of the lagenar and 

 saccular nerves to the labyrinth are similar in both genera. 



Between the ampulla of the posterior semicircular canal and the lagena cochleoe the 

 exoccipital sends in a process, which further back (Fig. 11) forms a complete roof for the 

 fovea for the inferior part of the labyrinth. 



Important differences are to be noted in Fig. 11, which falls through the plane of 

 escape of the vagus. In the first place the cavum sinus imparis is observed to have its 

 floor formed by the basi- and ex-occipitals, while its lateral walls are formed by the 

 stapedes and its roof by an ossified plate of dura mater entirely unconnected with the ex- 

 occipitals. How different this is in Amiurus may be seen by reference to Figs. 4, 5, 6, T, 

 PI. VI, loc. cit. Here the stapedes come chiefly in relation to the cavum sinus imparis, there 

 chiefly in relation to the atria sinus imparis. The explanation of this remarkable differ- 

 ence is to be sought for in the fact that the greater part of the Weberian apparatus has 

 been pushed (in the process of its reduction) into the foramen magnum, instead of being 

 entirely outside the skull, so that we shall find in Fig. 14, which represents a section 

 passing through the third pair of spinal nerves, that also the basioccipital, exoccipital, 

 and epiotic bones are met with ! We shall see that the three anterior centra, with the 



