OF DIDELPHYS VIRGINIANA. 



135 



however, it should he stated that the flexor longus poUicis of the hand is absent, or at least 

 sends no tendon to the thumb, the fifth thumb tendon of the hand resulting from the con- 

 fluence of this muscle with the common digital flexor ; and that, as we have seen above, the 

 flexor longus pollicis of the foot is present as a distinct muscle, only its tendon is arrested 

 on its way to the great toe, and tied at the end to the tendon of the common flexor. Fur- 

 thermore, in view of the connection of this oblique tendon with the tendon of the flexor 

 longus pollicis, the muscle in question might be regarded as an accessory of the latter. 



Adductor pollicis. — (Fig. 35, A.) A thin, fan-shaped plane of fibres, lying below the 

 level of the interossei, stretching between the second and first metatarsals, converging to 

 be inserted with the inner head of the flexor brevis, into the inner side of the base of the 

 first phalanx of the great toe. 



Flexor hrevis minimi digiti. — (Fig. 35, e, cut off.) A thin, triangular plane of fibres of 

 considerable superficial extent, its origin stretching across the foot from the cartilage upon 

 the ball of the great toe to the base and part of the shaft of the fifth metatarsal, and also 

 attached to the plantar fascia. Insertion at inner side of the base of the first phalanx of 

 the fifth toe. This muscle may be found incompletely divisible into two parts, the inner 

 of which would represent an adductor minimi digiti. 



Abductor minimi digiti. — (Fig. 35, fZ.) A very distinct muscle, arising by a short, 

 stout, fleshy belly from the under surface of the tuberosity of the os calcis, running along 

 the external border of the foot, to be inserted into the outside of the base of the fifth toe. 



Galcaneo-metatar sales. — These are two little flexing, or rather abducting, muscles of the 

 fifth metatarsal itself, arising from the anterior part of the tuberosity of the os calcis, and 

 passing to the outside of the base of the fifth metatarsal. They fill the deep notch between 

 these two points, and floor the sheath through which the oblique flexor of the great toe 

 passes. 



Interossei. — The plantar interossei are of great size, forming a thick, soft cushion that 

 fills the concavity of the sole formed by the curved metatarsals from the bases to the apices 

 of these bones. That one upon the tibial side of the second toe is perfectly distinct from 

 the others ; the rest are much blended together. The tendons have the usual lateral inser- 

 tions into the bases of the toes. They mostly embrace sesamoid bones. 



PART III. — ON THE ANTERO-POSTERIOR SYMMETRY, OR LONGITUDINAL 

 HOMOTYPY, OF THE MUSCLES OF THE LIMBS. 



The foregoing account of the opossum's bones and muscles, as little more than a mere 

 congeries of fiicts and observations, would appear fragmentary and pointless, were not at 

 least the attempt made to deduce some of those generalizations that belong to the field of 

 philosophic anatomy. Iri preceding pages certain morphological and teleological questions 

 have been neither specially sought nor avoided, but treated, when they seemed naturally to 

 arise in the course of the investigation, with whatever of light the writer's studies have 

 afforded. Such, notably, have been the considerations touching the morphology of the 

 skull regarded as a series of vertebrae ; the correspondences of the bones of the fore and 

 hind limbs ; the general homologies of certain muscles, and, more especially, the teleological 



