720 DR. W. B. CAEPENTER ON THE STRUCTURE, PHYSIOLOGY, AND 



cuous in the first five, every one of which may be readily distinguished from any other 

 and it will be desirable, therefore, to describe each of these separately. 



47. First Brachial. — It has been already shown (§41) that the inequality between the 

 lengths of the inner and the outer margins of this segment (Plate XXXVI. fig. 4, c, d) 

 is so considerable as to compensate in gi-eat degree for the extreme obliquity of the 

 distal face of the Third Radial, to which it is articulated; and is such as even to 

 occasion a curtailment of the inner half of each articular surface (fig. 4, a, c). The 

 proximal articular surface (a) presents on its outer side no special peculiarity ; but on 

 its inner side we notice at the inner extremity of the fossa for the interarticular ligament 

 a peculiar rounded pit (g), which might be supposed to be the socket for the articulation 

 of a pinnule. This, however, is not the case ; for no pinnule is borne by this segment, and 

 the articular sockets of the pinnules are always found on the longer sides of the Brachial 

 segments. The muscular fossse are carried so far back by the recession of the vertical 

 lamellse which bound them, as to form the greater part of the ventral face of the s^ment 

 (fig. c, c, c). The distal face (b) is formed on the plan of that of the Second Radial 

 (§ 37) ; being simply divided by a vertical ridge {a, a) into two lateral fossae {b, b), in 

 which are lodged interarticular ligaments, but no muscles. 



48. Second Brachial. — This segment presents a certain degree of resemblance to the 

 preceding in general form, and, like it, has its outer margin so much longer than its inner 

 as to produce a considerable obliquity between its articular surfaces (Plate XXXVI. 

 fig. 5, c, d). But it is here the proodmal face (a) articulating with the First Brachial, 

 which is divided (like that of the Third Radial, § 38) by a vertical ridge into two lateral 

 fossse ; whilst the distal (b), which articulates with the Third Brachial, bears a general 

 resemblance to the proximal face of the First, but is at once distinguished by the exca- 

 vation of its outer and upper portion (trenching on the outer muscular fossa) into the 

 articular surface for the first pinnule {p, figs, b, e). But for this difierence, the Second 

 Brachial might be easily mistaken for the First Brachial of the other arm of the same 

 ray. 



49. Third Brachial. — ^The general form of this segment (Plate XXXVI. fig. 6) is 

 more discoidal than that of either of the preceding ; but it still has a decided obliquity 

 (figs. C, d) between its proximal and its distal articular surfaces, which is, however, in 

 the contrary du-ection to that of the First and Second Brachials (Plate XXXVII. fig. 3). 

 The proximal face (a) presents the usual arrangement of fossae for the lodgment of 

 muscles and ligaments ; the surfaces for the attachment of muscles being here chiefly 

 provided by the two rounded lamellae which project from the upper or ventral margin 

 of the segment {d, d, figs, a, b). The distal face (b) shows a peculiarity of conformation 

 which we have not yet encountered ; for it is unmarked by any prominent ridges or fossae, 

 being in fact almost flat, except that it presents a series of slightly elevated ridges with 

 alternating furrows, which radiate from the opening of the central canal towards the 

 dorsal margin. The union of this face with the opposite face of the Fourth Brachial 

 (sg, figs, c, D, e) constitutes what was designated by Professor J. Muller a syzygy. 



