IN THE LIMBS OF MAMMALIA. 77 



extremity take their fixed point of action at the distal instead of the proximal ends of the 

 several segments, and the accessory long flexors of the leg are evidently more important 

 as mutually counteracting, and thus as balancing flexors and extensors of the pelvis, than as 

 either direct flexors of the leg or indirect extensors of the thigh. 



The direct extensors of the foot are, in man, very large, and two of them, the gastroc- 

 nemius and the soleus, with the enormously developed tarsal bone, upon which they are 

 inserted, seem to bear relation to the above-named physiological necessity ; however, they 

 are very good long and short muscles accessory to the tibialis posticus and the peronams 

 longus, which seem to be the morphological short and long extensors ; and in the A'i, 

 (Bradypus tridactylus,) the latter muscle does actually take part of its origin above the 

 knee-joint* 



The short flexor of the foot is the tibialis anticus, and the long the peronceus brevis, which 

 in man is also made to act as an extensor by its tendon passing behind the outer 

 malleolus, which, however, like the lower extremity of the fibula, is by no means constant 

 in mammalia. 



The toes are provided with a short and a long flexor, — flexor brevis digitorum, and flexor 

 longus digitorum, — and with a short and long extensor with corresponding names ; but the 

 morphology of these, and their relations to those of the fingers, will be more easily learned 

 from some animals in which there is more resemblance between the carpus and tarsus 

 without any such prominence of one bone of the latter, as in most mammalia, and espe- 

 cially in man. 



The following table may serve as a contribution toward a more complete understanding 

 of the correspondences between the muscles of the anterior and posterior extremities: — 



ANTERIOR. POSTERIOR. 



Latissimus dorsi, ? 



ji < Pectoralis major, Pectinasus, 



Teres major, Scansorius, 



Subscapularis, Iliacus, 



Teres minor, Gluta^us minimus, 



Infra-spinatus, Glutaeus medius, 



< [ Coraco-brachialis, Adductors, 



■\ Deltoid (spinal), Glutoeus maximus (sacral), 



. ( Deltoid (scapular), Gluteus maximus (iliac), 



<" / "^ "1 Supra-spinatus, Psoas magnus, 



Biceps, Biceps (ischiatic head), 



i< 1 







£, f Epitroclilien, Sartorius, 



Gracilis, 



Semimembranosus, 

 Semitendinosus, 

 " Brachialis anticus, Poplitaeus, 



i, f Supinator longus, Biceps (femoral head), 



£ J Pronator radii teres, 



% | Supinator brevis, 



< [ Pronator quadratus, 



Triceps, (scapular head), Triceps (rectus or iliac head), 



Triceps, (humeral heads), Triceps (vasti or femoral heads), 



*Meekel, "Traite Generale d'Anatomie couiparee." Tome vi. page 413. 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. 20 



