BIOLOGY. 263 



cent segments consist of the pharynx, the larynx, and a vertebra 

 enclosing part of the neural column, so also the skull, which is the 

 termination of these three organs, and where their outlets are vis- 

 ible, must consist of them also. The brain-case, therefore (the 

 termination of the neural system), is a modified vertebra, the 

 bronchial circle of nasal and palatine bones a modification of the 

 trachea, and the lower jaw a modified rib developed by the mouth. 

 The respiratory circle of bones is the key to the skull." 



HOMOLOGIES OP SOME OF THE MUSCLES IN FISHES. 



M. Baudelot (" Comptes Rendus," June 10, 1867) communi- 

 cates an interesting paper on the homology of the slender muscles 

 in fishes, situated, above and below, in the interval between the 

 two great systems of muscles which extend from the tail as far as 

 the scapular arch. He points out the relation between these mus- 

 cles and the median line fins, dorsals and anal. When there is a 

 continuous dorsal fin from the head to near the tail, there is on the 

 upper region only a single pair of these slender muscles, extend- 

 ing between the end of the single dorsal and the first rays of the 

 caudal. When the dorsal is very short, as in the pike and carp, 

 there are two pairs of these muscles, one in front of, and the other 

 behind the dorsal. When there are two dorsals, as in the trout, 

 there are three pairs of these muscles, one in front of each dorsal, 

 and the third behind the second dorsal. In the flounder, where the 

 dorsal extends the whole length of the back, these slender muscles 

 are not found. The same variations are observed in the abdom- 

 inal region in regard to the anal fin. 



He shows that these slender muscles are only the motor muscles 

 of the fin rays, whose fasciculi become consolidated into a single 

 longitudinal bundle when the rays which serve to support them 

 are absent or rudimentary. There can be seen a gradual passage 

 from the ray muscles to the slender muscles. 



He lays down the following formula in philosophical anatomy : 

 given on one hand a series of homologous bones, and on the other 

 a corresponding series of muscular bundles inserted into them, if 

 a certain number of the bones are absent, the corresponding mus- 

 cles are not at the same time wanting, but are united so as to form 

 a complex muscle. He illustrates this by the costal system of 

 mammals. In these the ribs cease at the beginning of the abdom- 

 inal region, but the muscles which would be attached to them do 

 not disappear, but are united to form the muscles called the exter- 

 nal and internal oblique and transversalis of the abdomen. The 

 external oblique is the union of all the external abdominal inter- 

 costal muscles ; the internal oblique of the internal abdominal in- 

 tercostals ; and the transversalis of the muscles corresponding to 

 the triangularis sterni. The recti muscles of the abdomen he re- 

 gards as the h6mologues of the inferior slender muscles, which in 

 fishes extend from the pelvis to the scapular arch. The different 

 muscles of the neck may also be considered as representatives of 

 costal muscles. 









