132 ON THE HOMOLOGIES OF CERTAIN MUSCLES 



deltoid ridge, d, and the scapulo-coraeoid fissure, and it is inserted 

 just where the pectoral ridge sinks into the articular head of the 

 humerus, proximally to the tendon of the teres minor. The supra- 

 scapular muscle is not ordinarily differentiated in reptiles into an 

 infra- and supra-spinatus. But in a gecko, Platydactylus, sp. ?, I 

 have observed it to take origin from the coracoid, as well as from 

 the scapular region of the shoulder-girdle ; and by doing this, it 

 has brought itself by origin, as it is often by innervation, into close 

 correspondence with the coraco-brachiales muscles, and, serially, with 

 the iliacus of reptiles. 



The muscle seen in fig. 4, intercepted between the tendon of the 

 biceps and that of the pectoralis secundus, is called ' deltoides in- 

 ternus ' by Meckel ; it is, however, obviously homologous with an 

 upper segment of the coraco-brachialis as seen in fig. 3 from the 

 crocodile, and with the ' short coraco-brachialis ' or ' rotator humeri ' 

 of Wood (' Journal of Anatomy and Physiology,' Nov. 1866, p. 49). 



The muscle described by Mr. Mivart in the Iguana tuberculata, 

 under the name of ' gracilis,' and stated by him to ' represent pos- 

 sibly the gracilis of mammals/ seems to me to be a serial homologue, 

 which I have not met with elsewhere, of the pectoralis major. It 

 arises from 'the ischiatic symphysis' (where, in the saurians, an 

 ossific nodule, the os cloacae, may not rarely be found placed 

 mesially, as though representing a sternum), and 'from the long 

 tendinous arch which passes from the front of the acetabulum, 

 round behind the pubic spine, back to the symphysis just mentioned.' 

 This latter origin seems to me to correspond with the intercla- 

 vicular and clavicular origin of the pectoral, as seen in some of the 

 Sauropsida, and, as far as regards the clavicle, in mammals. Its 

 insertion into the peroneal side of the head of the tibia seems to me 

 to be paralleled by the insertion of the pecto- antebrachial of certain 

 mammals, e.g. the cat (see Straus-Durckheim, vol. ii. p. 352, pi. vii. 

 figs. 13, 15). Mr. Mivart, by lettering his tibial adductor S, may 

 be understood, perhaps, to mean that he considers this muscle 

 homologous with the sartorius of anthropotomy ; and in this identi- 

 fication I should coincide. But the gracilis, which he seems to 

 think may perhaps be represented by the muscle I suppose to be 

 homologous with the pectoralis major, I think must be represented 

 by a head which the tibial adductor in the Iguana tuberculata 

 examined by me received from the symphysis of the ischia. 



