THE SIGNIFICANCE OF HUMAN ANOMALIES. 729 



Muscular System. — The muscular system of man is liable to 

 many variations, nearly all of which are interesting from a morpho- 

 logical point of view. 



B 



Pio. 8. 



■A, Normal ARBANOEirENT ; B, Abnormal Arrangemitnt. J. J., jugular veins from 

 head ; S. S., subclavian veins from arms ; V. C, vena cava ; H, heart. 



It is not uncommon to find in man useless rudiments of muscles 

 which exist in a well-developed state in some of our more humble fel- 

 low-creatures, and in them serve a definite purpose. 



In man the " skin-muscles " are very feebly developed compared 

 with those seen in many of the lower animals. The only remnants of 

 these in man are, the muscle which wrinkles the forehead (occipUo- 

 frontalis), the muscle immediately under the skin covering the side of 

 the neck {platysma myoides), and the palmaris brevis, a. little bundle 

 of muscular fibers in the palm of the hand ; not unfrequently rem- 

 nants appear abnormally in other situations, as, over the breast (see 

 Fig. 9), in the arm-pit, on the back, etc. The skin-muscles are well 

 developed in those of the mammalia which have loose skins, as, for 

 example, the hedgehog, porcupine, and porpoise. In the hedgehog, 

 when the skin-muscles contract, the animal becomes rolled up as in a 

 bag of muscles. The sportive gambols of a school of porpoises are 

 effected by an abundant supply of these skin-muscles ; in the horse 

 the skin-muscle is called the panniculus carnosus, and every one who 

 has seen a horse twitching its skin to get rid of troublesome flies will 

 easily understand how serviceable it is to that animal. 



In all human beings there is a small muscle going from a hooked 

 process (coracoid) on the upper end of the shoulder-blade to the inner 

 side of the arm-bone about the junction of its upper and middle third. 

 Sometimes this muscle is continued down to the lower end of the 

 arm-bone ; or, again, it may be quite short, and attached to the bag 

 of fibrous tissue covering the shoulder- joint. On referring to the 

 anatomy of the lower animals, it is found that both these varieties 



