402 MR. ST. G. MIVART ON THE ANATOMY OF ECHIDNA HYSTRIX. 
the same surface as that occupied by the infraspinatus, while the rest of it is but very 
slightly separated from the supraspinatus. 
The condition presented in the Echidna might be represented by a further modification. 
In that animal I find no trace of a ridge on the inside of the scapula like that which, in 
the Ornithorhynchus !, separates the supraspinatus from the subscapularis ; but the supra- 
spinatus is, nevertheless, separated from the subscapularis by a very large lamella, 
which throws the last-mentioned muscle entirely to the outer side of the scapula, and is 
the only one developed except that separating the supra- from the infra-spinatus. 
'The foregoing considerations suggest themselves from an examination of this most 
interesting mammal; but I am far from supposing that what has been here stated is 
sufficient to establish the myological homologies above suggested, which would require 
a fresh and. eareful study of all the main conditions presented by the limbs of the Ver- 
tebrata, especially of Reptiles and Amphibians, for their satisfactory demonstration. I 
cannot but think, however, that some cause has been shown for the promulgation of the 
hypothesis, and possibly enough to warrant further inquiries respecting this long- 
debated and interesting question of serial homology. 
! Professor Owen says, * In the Echidna this ridge is nearly obsolete," Todd's * Cyclopædia,” vol. iii. p. 376. 
EXPLANATION OF THE PLATES. 
Prare LII. Muscles of fore limb of Echidna hystrix. 
Fig. 1. Outer surface of left fore limb. R. Rectus abdominis. 
TZ. Trapezius. P. Pectoralis. 
L.D!. Latissimus dorsi (posterior portion). E.H. Epicoraco-humeral. 
L.D?. Latissimus dorsi (anterior portion). D!. Deltoid (first portion). 
D.E. Dorso-epitrochlear. D2. Deltoid (second portion). 
S.M. Serratus magnus. S.S. Supraspinatus. 
T.M. Teres major. LS. Infraspinatus. 
S. Subscapularis. C.B. Coraco-brachialis. 
LS. Infraspinatus. B. Biceps. 
D?. Deltoid (second portion). E.C. Extensor communis digitorum. ` 
T. Triceps. E.M.P. Extensor ossis metacarpi pollicis. 
E.R.L. Extensor radialis longior. E.R.L. Extensor carpi radialis longior. 
E.R.B. Extensor radialis brevior. E.R.B. Extensor carpi radialis brevior. 
E.M.P. Extensor ossis metacarpi pollicis. P.T. Pronator teres. i 
E.C. Extensor communis digitorum. F.R. Flexor carpi radialis. 
E.M.D. Extensor minimi digiti. F.U. Flexor carpi ulnaris. 
E.U. Extensor carpi ulnaris. Fig. 3. Flexor surface of left forearm and hand. 
FU. Flexor carpi ulnaris. F.C. Flexor communis digitorum. 
À EU. Panniculus carnosus. F.R. Flexor carpi radialis. 
Fig.2. Front view of left shoulder and arm. L.D!. & F.U. Conjoined posterior part of 
S.M. Sterno-mastoid. Latissimus dorsi and Flexor carpi une 
