i;^4 anatomy in a nutshell. 



The Coccyx. 

 The coccyx is formed by four and sometimes five segments. It has no 



SPINAL CANAL, [NTERVERTEBRAL FORAMINA. SPINOUS PROCESSES, LAMIN.E, PED- 



[CLES. The firsl segmenl may be separate bu1 the rest are united and run to a 

 point. This bone has an anterior and posterior surface, two borders, a base, 

 and an apex. 



The anterior surface has three transverse grooves marking the union of the 

 ments. This surface is concave. 



The posterior surface is convex and has grooves similar to those on the an- 

 terior. The upper cornua are large and articulate with thecornua of the sacrum 

 making the fifth posterior sacral foramina. 



The lateral borders are thin and present small eminences — the rudimentary 

 transverse processes. The upper pair of the processes may articulate with the 

 inferior lateral angles of the sacrum, thus forming the fifth anterior sacral for- 

 amina. The other processes are small and may be absent. 



Blood Supply: — Sacra media. 



( )ssification: — Four centers. 



Articulation: — With the sacrum. 



Attachment of Muscles: — Four pairs and one single muscle; on either 

 side, the Coccygeus; behind, the Gluteus maximus and Extensor coccygeus, 

 when preseni ; at the apex, the Sphincter ani; and in front, the Levator ani. 



LESSON XXXV. 



Psoas magnus. — Description. — (Plate LXXIII.) In the posterior part of 

 the substance of this muscle, the lumbar plexus is situated. This muscle, which 

 is placed on each side of the spine in the lumbar region and the margin of the 

 pelvis, is a Long and fusiform one. It is attached by five slips to the interverte- 

 bral substance and the adjacent parts of the vertebra above and below. Be- 

 tween these slips are tendinous arches which with the concave part of the body 

 of each lumbar vertebra make a passage for the lumbar vessels and filaments of 

 the sympathetic nerve. As the muscle passes down it decreases in size and 

 passing under Poupart's ligament, it terminates in a tendon after having re- 

 reived nearly all the fibers of the Iliacus. 



Origin: — (Plate LXXIII.) (1) Front of bases of lumbar vertebrae by 

 live fleshy slips; (2) -ides of bodies and intervertebral substances of last dorsal 

 and all the Lumbar vertebrae. 



Insertion: (Plates XLVIII-XLIX.) Lesser trochanter of the femur. 



A( pion: 1'lexes thigh on pelvis; maintains erect posture. 



N i RVE Si I'i'iA : Anterior branches of second and third lumbar nerves. 



Blood Si pply: — Dio-lumbar from posterior branch of internal iliac, and 

 lumbar from abdominal aorta. 



Psoas parvus. Description.— (Plate LXXIII.) This muscle may be 

 absenl or double. It is situated in front of the Psoas and ends in a long flat 

 tendon. It is well developed in those animals which are swift runners, in that 

 it flexes the pelvis and arches the Lumbar spine. 



