614: Mr. T. P. Buist on the Devdopment of 



fishes^ especially in the peculiar proportions of the coraco- 

 scapular skeleton. The main part of the coraco scapular 

 skeleton is a triangular cartilaginous plate, the " intermediate 

 cartilage/' attached by its apex in front and below to the 

 ossified coracoid and above and behind by its base to the 

 small scapula and four proximal radials, also ossified. 



The coracoid (fig. 1) consists of two main limbs, forming 

 a somewhat obtuse V, and of a smaller arm within the angle 

 of the V, One limb {pt p) is directed backward, tapered at 

 its posterior extremity, and attached internally by a flattened 

 surface to its fellow of the opposite side. The other limb 

 {pr.p') is slighter and wedge-shaped ; it passes upward and 

 outward and articulates with the posterior aspect of the 

 inner branch of the stem of the clavicle. The arm of the 

 coracoid divides the angle into two unequal parts, the upper 

 being the smaller, and is directed upward, backward, and 

 outward to join the apex of the intermediate cartilage. 



The proximal radials are four ossicles with slender middles 

 and expanded proximal and distal extremities. The distal 

 extremities bear pairs of small ragged processes, carrying the 

 distal radials, and also minute recurved processes wliich 

 anchor the ossicle to the lips of the cleft in the dermal 

 armature through which the fin passes. 



The scapula is similar to the proximal radials, but its 

 distal extremity is expanded into tM'o arms, the upper and 

 anterior being attached to the clavicle, while the posterior 

 articulates with the distal extremity of the upper proximal 

 radial. 



The clavicle is roughly T-shaped ; the upper part is 

 attached internally to the transverse processes of the first 

 and second vertebrae, while the stem forks and the branches 

 are attached to the jugular plate. Through the two foramina 

 thus formed a pair of muscles pass forward from the trunk, 

 and, after joining to form a single median tendon, are 

 inserted into the urohyal. 



Owing to the difficulty of procuring the requisite material 

 a complete range of embryonic stages has not been available, 

 and a description of the earlier stages has therefore had to be 

 omitted. The figures were prepared from serial sections by 

 the contour method of reconstruction ^. Ehrlich's acid ha3ma- 

 toxyliu followed by orange G in 70 per cent, alcohol as a 

 slide-stain was used in the preparation of the sections. 



Stage I. — The youngest stage procured, 21 mm., was 

 taken from the pouch of a specimen from the University 



* T. P. Buist, " A Method uf llucoustructi'ju by Coutours," Joura. 

 Auat. & Plus. vol. xlvii. (1913). 



