484 DR. W. G. EIDEWOOD ON THE CRANIAL [DeC. 13, 



of the supraoccipital, there is a large depression at the back of the 

 cranium between the two epiotics. This is not subdivided by a 

 median crest of the supraoccipital, but a supraoccipital spine lies 

 dorsally to it, and splits up posteriorly into seven oi- eight fine 

 bony filaments, compared by Hyrtl {I. c. p. 3) with the ossified 

 tendons of birds. The two exoccipitals ai'e pi'oduced backward 

 and upward into pointed plates, which form a roof not only for 

 the medulla, oblongata, but for the anterior part of the spinal cord 

 as well. 



The squamosal is produced into a spine which slopes backward, 

 outward, and downward, and extends to the posterior end of the 

 post-temporal. The opisthotic is small, and is apj)lied to the 

 inner side of the basal portion of this spine, but it also touches 

 the exoccipital. The articular surface for the head of the hyo- 

 mandibular slopes downwai'd and forward. The lateral temporal 

 groove above the postfrontal spine is to a large extent roofed over 

 by projecting eaves from the fi'ontal and squamosal bones, mainly 

 the former. Incision into the squamosal and pro- otic bones fails 

 to disclose the presence of bullae for the lodgment of caecal 

 diverticula of the swim-bladder. There is no subtemporal fossa. 



There is no orbitosphenoid nor basisphenoid. The parasphenoid 

 is rather sharj^ly bent at about the middle of its length, and at 

 this point thei-e is on the ventral surface a well-marked oval 

 depression. The ascending wings of the parasjjhenoid rise 

 moderately high up the front of the pro-otics. The parasphenoid 

 does not extend as fai- posteriorly as the hind end of the basi- 

 occipital, and the eye-muscle canal does not open behind. Neither 

 the parasphenoid nor the vomei- bears teeth. A considerable 

 pi'oportion of the ethmoid region remains cartilaginous. The 

 23i'ef rentals do not meet one another mesially, and the mesethmoid 

 is a thin horizontally disposed lamina of bone of ectosteal origin. 



Projecting backward and outward from each side of the back 

 of the cranium are two strong tendon-bones, or intermuscular 

 bones. The larger of the two arises from the dorso-latero-posterior 

 part of the basioccipital, and is attached to the upper end of the 

 clavicle. The other arises from the back of the exoccipital, 

 immediately posterior to the aperture for the exit of the vagus 

 nerve, and terminates in muscular tissue. The deep limb of the 

 post- temporal, attached to the opisthotic, is parallel to these, and 

 its resemblance to them is veiy striking. 



Tertiporal and Preopercular Series (text-fig. 141, p. 485). — The 

 post-tempoi-al tends to fuse with the supraclaviculai-. Its upper 

 limb is long, and lies so far over the epiotic as to touch the supra- 

 occipital. The deep limb is about half as long as the foi-mer and 

 is attached to the opisthotic. A study of the skull of (Jhanos 

 leaves little room for doubting that the opisthotic limb of the 

 post-temporal belonged primarily to the same category as the 

 tendon-bones that project back from the exoccipital, but has now 

 become united by its posterioi' end with the post-temporal bone 

 (see preceding paragraph). 



