THE LUMBRICALES 335 



Insertion. — The deep surface of the skin and the sulxaitaneous fat, along the 

 nhiar border of the ui)per part of the ])ahn. 



Structure. — Arising l)y tleshy and sliort tendinous fi1)res, tliis muscle passes in 

 transverse fasciculi to its insertion, which is of a similar character to its origin. 

 It belongs to that t3'pe of muscle of which the i)anniculus carnosus in the 

 mammalia is the best example, and lies in the subcutaneous tissue superficial to 

 the deep fascia like the platysma myoides and the superficial muscles of the face. 



Nerve-supply. — From the inner cord of the brachial plexus (through the first 

 thoracic nerve), by filaments from the superfi(;ial division of the ulnar nerve which 

 enter the muscle upon its deep aspect near its upper border. 



Action. — It draws the skin and the superficial fascia of the ulnar border of the 

 hand towards the middle line of the j)ahn, forming a deep dimple or groove upon 

 the upper part of the ulnar border of the hand, and at the same time raising the 

 soft parts into a prominent vertical ridge, the object of which appears to be to pre- 

 vent the ulnar nerve and artery from l^eing pressed upon when a hard substance is 

 grasped by the hand. It also helps to deepen the cup-shaped hollow when the 

 palm is used to conve}^ fluid to the mouth. 



Relations. — Superficially, the skin; deeply, the hypothenar fascia, which 

 separates it from the abductor and flexor brevis minimi digiti, and from the ulnar 

 vessels and nerve. 



Variations. — This muscle may be entirely absent. 



Deep Muscles of the Palm of the Hand 



Cexteal Group 

 Consisting of two sets of muscles — the lumbricales and the interossei. 



1. THE LUMBRICALES 



The lumbricales — named from their resemblance to earth-worms ( =Iumhru'i) 

 — are four small muscles of a fusiform shape. 



Origin. — The two outer ones from the outer side of the first and second tendons 

 of the flexor profundus digitorum; the two inner from the adjacent sides of the 

 second and third, and third and fourth tendons of the flexor profundus digitorum 

 respectively. All four are attached to the palmar aspect of the deep flexor, and the 

 origin begins at the lower border of the anterior annular ligament. 



Insertion. — The aponeurosis of the extensor communis digitorum tendon on the 

 radial side of the first phalanx of each of the four fingers. 



Structure. — Arising fleshy from the tendons of the deep flexor, the fibres con- 

 verge upon a small tendon which becomes free a short distance aljove the metacarjjo- 

 phalangeal joint. The tendon passes in front of the deep transverse metacarpal 

 ligament, below which it expands, and is attached to the border of the extensor 

 tendon. 



Nerve-supply. — From the outer and inner cords of the Itrachial plexus; the 

 first and second receiving small filaments from the digital branches of the median 

 nerve, Avhich enter the muscle near tlie radial Ijorder in the middle third of their 

 palmar aspect. The third and fourth lumlnicales are supi)lied by filaments of the 

 deep l)ranch of the ulnar nerve, which enter their respective muscles in the middle 

 third of their deep surfaces. 



Action. — Their chief action Avill be (1) to flex the first phalanges upon the meta- 

 carpal bones; and at the same time (2) to extend the second and third phalanges 

 by their traction upon the sides of the extensor ai)oneurosis which covers the back 

 of each of the first phalanges. In this action they assist the interosseous muscles; 

 but the lumbricales have this advantage over them, that when the second and third 

 phalanges are flexed by the flexor sultlimis and ]n-ofundus, the lumbricales will flex 

 the first phalanges with increased force, inasmuch as the tendons from which they 



