112 E. EAMSAY WEIGHT ON THE SKULL AND AUDITOEY 



other (except for a persistent median strip of cartilage) iu the middle line, and carry as 

 usual ou their ventral aspects the fossce for the articulation of the palatine arch. 



A slender vomer invests the strip of cartilage referred to from below, and extends for- 

 ward towards the middle of the papyraceous mesethmoid, which forms a considerable part 

 of the thin vaulted roof of the mouth of this remarkable genus. The mesethmoid is separa- 

 ted from the parethmoid by persistent strips of cartilage, and is intimately united with the 

 premaxillaries which are coalesced in the middle line, are destitute of teeth, and partake of 

 the papyraceous texture of the mesethmoid. Right and left of the premaxillaries are the 

 maxillaries, slender rods which support the long maxillary barbels. On the upper surface 

 of the skull two further bones are met with, both sleuder and in contact with the sculp- 

 tured face of the parethmoid. These are the nasal and antorbital which shelter the fore- 

 most divisions of the neuromastic canals of the head, and are situated on the lateral and 

 mesal aspects of each nasal sac. The neuromastic canals enter them from the parethmoid, 

 the sculptured face of which is cousec|ueutly to be regarded as developed round these 

 canals. 



From Figs. 1, 2 and 3 some facts may be gleaned as to the form of the conjoined anterior 

 vertebrœ and the supraclavicles. In certain Nematognathi (the Hypostomidse) the fifth 

 vertebra has two kinds of transverse processes, one projecting outward from the junction 

 of neural arch and neural spine, the other from the centrum ; both unite laterally into a 

 single plate. The fourth transverse process in Hypophthalmus is somewhat similarly 

 formed ; it has a dorsal and a ventral lamella, which are contimied backward and later- 

 ally into a single plate, leaving between them a cavity in which lies the rudimentary air- 

 bladder. (Fig. 3). The lateral border of the dorsal lamella is quite sharp, and is coossified 

 with the epiotic process of the supraclavicle. At the junction of the dorsal lamella with 

 the arch are to be seen the foramina for the dorsal divisions of the fourth and fifth spinal 

 nerves, and these foramina serve to indicate the posterior limit of the third and fourth 

 neural arches respectively. The ventral lamella only abuts against the body of the vertebra 

 by a slender process (seen directly behind the basioccipital process of the supraclavicle in 

 Fig. 2), but is continuous behind with the more massive transverse process of the 

 fifth vertebra. Against the plate projecting backward from the union of the dorsal and 

 ventral lamelUe, the main part of the sui^raclavicle is applied like a splint : the lateral neu- 

 romastic canal enters the interval between these before becoming entirely surrounded by 

 the supraclavicle, and a fossa for the articulation of the shoulder girdle is left between 

 the point of the plate referred to, and the postero-lateral angle of the supraclavicle. A 

 similar fossa is found both in Amiurus and Aspredo, but in Liposarcus the supraclavicle 

 alone comes into relationship with the shoulder girdle. 



I have already drawn attention to the union of the supraclavicle with the skull ; 

 the union is suturai only with the basioccipital, but the epiotic and pterotic processes are 

 completely fused with those regions of the skull. Between these two is an aperture iu 

 the dried skull, which will be seen from Figs. 11 and 12 (which pass through it) to be uti- 

 lized for sending off" important cutaneous branches from the ueuromastic canal. If a bristle 

 be passed into this aperture in the macerated skull towards the hinder surfiice of the exoc- 

 ciptal, it can readily be caused to enter the cranial cavity through the large fenestration 

 through which the vagus escapes. 



Fig. 4 represents the opercular apparatus and jaws from the lateral aspect. The 



