ANATOMY IN A NUTSHELL. 109 



carpi ulnaris, Flexor ossis metacarpi minimi digiti, and Flexor brevis minimi 

 digiti. 



Metacarpal bones. — (Plate VII.) — Each one has two centers, one for the 

 shaft and one for the distal extremity, except the metacarpal of the thumb and 

 it has one for the proximal extremity. The nucleus for the shaft appears about 

 the eighth or tenth week of intrauterine life, and that for the diaphysis the third 

 year, uniting with the shaft about the twentieth year. Each phalanx has two 

 centers, one for the shaft "which appears the eighth or tenth week, and one for 

 the epiphysis between the third and fifth year, and joins the shaft the eighteenth 

 year. The epiphysis for each phalanx is proximal, so the nutrient artery runs 

 towards the distal end (Principle III, Lesson I). The center for the distal phalanx 

 is at the distal extremity of the shaft, while that for the other phalanges is at 

 the center of the shaft. The metacarpal of the thumb articulates with two 

 bones, viz.. trapezium proximally. and the first phalanx of the thumb distally. 

 It has four muscles attached, Extensor ossis metacarpi pollicis, Flexor ossis 

 metacarpi pollicis, Flexor brevis pollicis, and the First dorsal interosseous. The 

 second metacarpal articulates with five bones, the trapezium, trapezoid, and os 

 magnum proximally, the third metacarpal internally, and the first phalanx of 

 the index finger distally. It has six muscles attached, the First and Second 

 dorsal interossei. Extensor carpi radialis longior on the dorsal aspect of the bone 

 and the Extensor carpi radialis, First palmar interosseous, and the Adductor 

 obliquus pollicis on the palmar aspect of the bone. The third metacarpal artic- 

 ticulates with four bones, os magnum proximally, the second metacarpal ex- 

 ternally, the fourth metacarpal internally, and the first phalanx of the middle 

 finger distally. It has six muscles attached; on the dorsal aspect the Second 

 and Third dorsal interossei, and the Extensor carpi radialis brevior and on 

 the palmar aspect the Adductor transversus pollicis. Adductor obliquus pollicis, 

 and Flexor carpi radialis. The fourth metacarpal articulates with five bones. 

 os magnum and unciform proximally, os magnum and third metacarpal exter- 

 nally, the fifth metacarpal internally and the first phalanx of the ring finger 

 distally. It has three muscles attached; on the dorsal aspect the Third and 

 Fourth dorsal interossei, and on the palmar aspect the Second palmar inter- 

 osseous. The fifth metacarpal articulates with three hones, the unciform prox- 

 imally, the unciform and fourth metacarpal externally, and the lirst phalanx 

 of the little finger distally. It has five muscles attached; the Extensor carpi 

 ulnaris, Plexor carpi ulnaris, Third palmar Interosseous, Fourth dorsal inter- 

 osseous, and Plexor ossis metacarpi minimi digiti. 



Flood supply of the first metacarpal bone is derived from the princeps 

 pollicis artery; it enters on the ulnar side, and is directed towards the head 

 of the hone. 



For the second metacarpal bone, the nutrient artery P derived from 

 lirsl palmar interosseous. It enters on the ulnar side, and is directed towards 

 the proximal end or base of the bone. 



For the third metacarpal hone ih< nutrient artery is derived from the 

 interosseous; il enters as a rule, on the radial side and is directed towards 

 the base. 



