196 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



cular cornu is prolonged far forwards into a cartilaginous bar, re, wliicb 

 we may designate here as the rostral cartilage on account of its great 

 antero-posterior development. The cartilaginous investment of the 

 auditory capsule au is still imperfect. From the sides of the trabecular 

 floor upon which the brain lies, the palato-quadrate elements arise to 

 give attachment to the cartilages of the maxillary and h3^oid arches. 

 The metapterygoid cartilage mt extends outwards and downwards be- 

 hind and below the eye to articulate with the very long rod-like quad- 

 rate q, which articulates at its front end with the rudiment of the lower 

 jaw, Meckel's cartilage mlc. Above the articulation of the quadrate with 

 Meckel's cartilage a curious bent element, a?, ai)X)ears to represent the 

 superior maxillary. Just in front of the expanded upper extremity of 

 the maxillary lies the posterior extremity of the upper labial or inter- 

 maxillary element la, which is continuous with a similar i^iece on the 

 opposite side ; this intermaxillarj^ bar curves over the anterior upward 

 bend of the rostral cartilage re. It constitutes the skeletal boundary 

 of the upper part of the oral opening m', and is not segmented in the 

 median line so as to articulate with its fellow of the opposite side like 

 Meckel's cartilage of the lower jaw. 



The hyomandibular hm is not well differentiated from the metaptery- 

 goid; \r> fact, the point where the quadrate and metapterygoid are seg- 

 mented is only faintly indicated, as might be expected from the intimate 

 unions of these bones in later life, amounting almost to synostosis. The 

 symi^lectic sy is a slender rod somewhat impressed into the quadrate 

 externally at its upi^er end, and almost continuous at this stage with 

 the hyomandibular. The symplectic, like the quadrate, is seen to be 

 enormously elongated, as compared with its homologue in the normal 

 ichthyan skull of the same relative age. 



The skeletal elements of the lingual or hyoid arch are also modified 

 considerably. The ceratohyal cy is a flat, oval cartilaginous plate lying 

 against the inner side of the lower end of the hyomandibular and the 

 inner side of the upj)er end of the quadrate. It articulates at its lower 

 end with the rod-like hypohyal hhy. There appear to be no mesial hyal 

 elements at all, which also seems to be the case with the adult, the me- 

 dial skeletal elements of the tongue being suppressed. 



The branchial arches h' h" h'" h"" are present at this stage to the 

 number of four, the same as in the adult, and the lower mesial elements 

 ajjpear to be absent, just as in the case of the hyoid elements. The 

 branchial cartilaginous bars themselves are weak. 



Shonlder-f/irdle. — The breast or pectoral fins, at this stage, have a 

 high basis, as stated by Cope in regard to the adults, where, together 

 with the dermal plates of the throat, a firm i)ectoral arch or shoulder- 

 girdle is developed in which there is sutural or, at least, inflexible union 

 of the coraco-scai)ular elements, I have only indicated the outline of 

 this arch in the figure at cs ; the object was too opaque here to make 

 out the contour of its elements. The lower end is coracoid, and has 



