12i MOKPHOLOGY OF THE BOXES OF THE LIMBS. 



exists in the lower limb a double ventral branch (pubis and ischium) most 

 probably corresponding morphologically to the epicoracoid and coracoid of the 

 Monotremata and Reptiles. The clavicle has, indeed, by some been held to be 

 represented by Poupart's ligament, but it seems on the whole more probable that 

 there is no exact homologue of the clavicular arch in the lower limb. The 

 marsupial bone of the pouched mammals does not represent the clavicle, but lies 

 in the situation of the upper or mesial pillar of the external inguinal aperture. 



With regard to the comparison to be established between the individual parts 

 of the scapula and ilium, still gi'eater difficulty prevails than iu the general deter- 

 minations before mentioned, ^^^^en looked at only in man, the iliac fossa appears 

 at fii'st sight to be the most obvious representative of the subscajaular fossa; 

 while the dorsum ilii seems to contain within its limits parts corresponding to 

 both the supra- and infraspinal fossas. But when oiu- observation extends to a 

 series of different animals, this view loses its apparent probability, and a different 

 mode of comparison is forced upon us. It then appears obvious that the iliac 

 fossa does not at least correspond to the subscapular ; but the full determina- 

 tion of the homologies of the different parts of the scapula and ilium, is one of 

 the most difficult parts of this intricate subject. Two different views have lately 

 been brought forward, the one supported by Flower, according to which the 

 scapula and ilium are supposed to have undergone rotation with reference to 

 the axis of the limbs in different dii-ections, the scapula backwards, the ilium 

 forwards, in such a manner that the prescapular fossa (supraspinous of man) 

 corresponds to the sacral siu-face of the ilium, the postscapular (infraspinous of 

 man) to the iliac fossa or surface, and the subscapular to the gluteal. (See 

 Flower's '' Osteology of the Mammalia,"' and '• On the Correspondence between 

 pai'ts composing- the shoulder and the pelvic gndle of the Mammalia," Jouni. of 

 Anat., vol. iv.. 1870.) According to the other view maintained by Hunijihiy, 

 the prescapular and iliac fossEe are regarded as homologous, and the post- 

 scapular fossa as corresponding ■with the dorsum ilii or gluteal sui-face, the sub- 

 scapular siurface being represented by the sacral and the true pelvic siu-faces of 

 the ilium. (Humphry, '' Comparison of the Shoulder Bones and Sluscles with 

 the Pelvic Bones and Muscles." Journ. of Anat., vol. v. : see also Mivart, in Luin. 

 Soc. Trans. ISOti, and RoUeston, in the same, 18(J9). In the more developed 

 forms of the scapula and ilium, in which the muscular fosste are of large extent, 

 it is almost impossible to trace the relations now refeiTcd to ; but in the com- 

 parison of the simple forms of these bones which belong to some animals with 

 those of others throughout the series, resemblances are perceived which give to 

 the ^'iews of Flower the greatest share of probability. In such simpler forms of 

 scapula and ilium these bones may be described as three-sided prismatic rods, in 

 which an internal surface is separated from two external surfaces by anterior 

 and 230sterior ridges, and the two external surfaces are divided by an external 

 ridge which descends from the dorsal extremity of the bones to the ca^dtj' of the 

 joints. It is in this external ridge, glenoid in the scapula and cotyloid in the 

 ilium, and which includes in both the attachment of the great extensor muscle of 

 the limb, that the key to the homologies of the bones is probably to be found. 

 Further observations, especially on the disposition of the muscles, are necessary 

 to detennine this question satisfactorily. 



Bones of the Limbs. — In making the comparison of the bones composing the 

 limbs themselves, it may be proper to revert to the simpler relations subsisting 

 between the limbs and the trunk or vertebral axis of the body in earlier 

 embryonic life, and to remind the reader that there is a determinate and similar 

 position in which the elements of the limb-fonning parts are developed from the 

 side of the vertebral stem or tiomk (Humphry). In the very earliest stage, while 

 the embryo still occupies the jn-one jiosition in the blastoderm, the limbs may be 

 said to bud out laterally from the dorsal plates as flattish semilunar flaps, so that 

 they present a dorsal and a ventral surface, coinciding with these respective 

 surfaces of the trunk : but in the next stage, when the Hmbs come to be folded 

 against the body in the ventral dii'ection, although the original relation to the 

 trunk is undisturbed, tlieu- axes have now come to lie nearly perpendicularly to the 

 transverse plane of the vertebral axis, and the position of the limbs is such that in 

 each there is one Ijorder which looks towards the head, and another which looks 



