74 SPECIAL ANATOMY. 



Ossification commences with the fortieth day of foetal life ; a year after 

 birth the two lateral portions first unite together, in the arch, and only in the 

 third to the fourth year with the body ; the ossifying points of the transverse 

 and spinous processes are first united in the twentieth to the twenty-fifth 

 year. 



In the Sacrum and Coccyx ossification commences, first in the body, in the 

 second to the third month ; the junction of the many ossifying points takes 

 place very late, sometimes not at all. From the fortieth to the sixtieth year 

 the coccyx usually unites with the Sacrum, but it is generally more slow in 

 females than in males. 



83. Thoracic cavity, chest, thorax s. pectus. 



Situation : between the seventh cervical and first lumbar verte- 

 brae, below the clavicle. 



Figure : conical, the base below, the obtuse apex turned to- 

 wards the neck, flat from before to behind. 



Parts: 1. Dorsal vertebrae, vertebrae dorsales, twelve; 2. 

 Breast bone, sternum; 3. Ribs, costse s. pleurse, twenty-four. 



84. I. Sternum s. os pectoris, Breast bone. 



Position : anterior, central part of the chest. 



Shape: flat, sword-shaped, above broad, one and a half to two 

 inches, below, narrow, rounded ; before, somewhat convex; be- 

 hind, rather concave. Length, from five and a half to seven arid 

 a half inches; thickness, above, six lines; below, three lines. 



1. Manubrium Sterni, handle, the most superior piece, for m. sterno-hyoidei, 

 thyreoidei, mastoidei. 



a. The superior border, concave, called incisura semilunaris, s. Furcula 

 (Vogel) ; on either side Incisura clavicular is, an oblong articular surface for 

 the clavicle. 



b. Lateral borders, longer; with Foveae articulares for the first and second 

 ribs. 



c. Inferior limit, a transverse line, the commencement of the body, where 

 the second rib attaches. 



2. Corpus, s. Macro, middle piece, for m. triangularis and pectoral, major, 

 the longest portion. Foveae articulares, for 3 to 7 ribs. Transverse line. 



3. Processes ensifurmis, s. xyphoides, ensiform process, termination of the 

 breast bone, for m. rectus abdom., Diaphragm, flat, blunt pointed or forked at 

 the end, generally cartilaginous, with one, sometimes two holes, for art. mam- 

 rnar. intern. 



Structure: within, spongy; without, compact substance, cov- 

 ered with membr. propria sterni. 



Development : Ossification commences late in the manubrium, 

 about the fifth to the sixth foetal month, in the spaces between 

 the extremities of the ribs. In the fifteenth to the sixteenth year 

 there are five to six, later only three pieces to be seen. Ossicula 

 episternalia, according to Breschet, rudimentary ribs, are some- 



