36 SHOULDER-GIRDLE AND BREAST-BONE. 



precocious inter-clavicular splint, although in the other types of the Plectognaths the existence 

 of this splint is doubtful, the place being evidently supplied by periosteal growths from the large 

 coracoid. 



The brachial series of bones (fig. 4 B, b. 1 5) are much more strongly ossified than their 

 scapular foundation ; there are five of them, and all but the upper are elegantly hourglass- shaped ; 

 the upper bone is very irregular, oblong, and notched ; they occupy the whole posterior margin of 

 the scapula and prse-coracoid. The inter- clavicle wedges itself between the lowest bone and the 

 prse-coracoid, the lowest brachial sending down behind it a long periosteal process. They are all 

 rich in these outgrowths, and the narrowing of the waist of each bone arises from an arrested 

 cleavage into a prse-brachial and a post -brachial series ; the ectosteal sheath of the bone fits to the 

 contained cartilage, like a pair of corsets. 



Example 2. Tetrodon ? 



The small Spiny Globe-fish from which my dissections have been made 1 measures less than 

 three inches in its entire length. The Woodcut (figs. 4 C, 4 D) shows the outer and inner parts of 

 its Shoulder-girdle magnified six diameters, and the endo-skeletal elements are depicted as somewhat 

 disarticulated from their investing splints. 



In this instance, as in the Ostracion, the ossifications (ganoid spines) formed in the skin are 

 quite irrelative to those found in the subcutaneous tracts and in the aponeurotic septa, and which 

 are, by a sort of morphological affinity, correlated with the true skeleton. The splint-bones are 

 very fibrous, and the endo-skeletal parts are but feebly ossified. The post-temporal (fig. 4 C, p. t.) 

 is a triangular bone, the base of which is attached firmly to the angles of the occiput, whilst its 

 apex is produced outwards and backwards ; behind this spur there is a condyle for the supra- 

 clavicle, and on the upper margin the bone is notched. The supra-clavicle (s. cl.) is not unlike 

 the blade of a pruning-knife, its point being directed downwards, its sharp edge looking for- 

 wards ; its crescentic postero-superior edge is thickened, and the part to be joined to the " haft" is 

 the condyle, which is articulated with the supra-temporal ; whilst the blade lies obliquely in the 

 upper fossa of the clavicle. This latter bone (cl.) is normal, and like many other Fish-bones is 

 developed into wings. Of these there are three one growing inwards, concave in front ; another 

 outwards, convex in front ; and these together form the bony door to the hinder part of the gill- 

 opening. The third plate grows backwards ; it is convex on its outside and concave within ; it 

 is deficient both above and below, and is attached behind to the true Shoulder-girdle. Below, 

 the clavicle ends in a long style; above, it is scooped in front, and is obliquely emarginate. Behind 

 this part is the " upper post-clavicle," it is a gently curved style (figs. 4 C, 4D, u.p.cl.) with an upper 

 snag at the middle, and having the lower half scooped in front for the bone below. This next bone 

 is the " lower post-clavicle" (1. p. cl.) ; it articulates to the outside of the lower half of the upper 

 piece, and is an elegantly arcuate, slender style, which forms nearly a right angle with the 

 clavicle, and reaches as far downwards ; these bones lie within the true shoulder-plates (fig. 4 C.) 



It is not easy, at first, to see the meaning of the true Shoulder-bones in the Tetrodon, for it 

 has made a great stride towards the typical Fish, as may be seen by comparing it with the 



1 The gift of Dr. Giintber. 



