1024 



THORAX. 



may be either placed one above the other, 

 or side by side. In the former case the up- 

 permost nucleus is the larger ; in the latter, 

 both may be symmetrical and of equal size, or 

 what is more common, they may be of un- 

 equal magnitude. It may occasionally present 

 more than two osseous points. Albinus 

 found three in one subject, and four in 

 another.* Mr.Quain has a preparation in Uni- 

 versity College, where the very unusual num- 

 ber of six (fig. 660. c. V.) are to be seen. In 

 this case, where there is a plurality of osseous 

 points, the largest are generally situated alone; 

 exceptions to this rule are very rare. 



Ossification of the body, or the 2nd, 3rd, Uh, 

 and bth pieces. The osseous nuclei which 

 enter into the composition of the body of the 

 sternum have generally a rounded form when 

 they are single, and are situated in the middle 

 line ; where they are in pairs or are placed 

 laterally, they are more elongated, but smaller, 

 and appear to represent only the half of one 

 of the single nodules. The second piece has 

 not often more than a single granule (b. 2, 

 c. 2'.), but the rest are frequently formed from 

 two nuclei, which are placed laterally to one 

 another (c 3', 4'.), and not vertically as occurs 

 in the first piece. 



These different osseous points are always 

 so arranged as to be situated between two 

 costo-sternal articulations, so that a portion 

 of the sternum is developed in each of the 

 intervals comprised between the ribs. The 

 last piece is the only exception, being com- 

 mon to the articulation of the 6th and 7th 

 ribs. There are, therefore, four primitive 

 pieces of the body of the sternum (b. 1, 2, 3, 

 4.), and each of these is sometimes formed 

 by one point of ossification ; at other times 

 by two lateral points. The first piece may be 

 formed of one or many ossific points, which 

 may be arranged vertically as well as laterally 

 To the centres of ossification here described, 

 M. Brechet f has added two small epi-sternal 

 granules, whose position is sufficiently shown 

 by the indication of the'm, fig. 660. at d**. 

 They occur only at rather advanced periods 

 of life, but they do not appear to be constant. 



Union of the points of ossification of the body 

 of the Sternum. In considering the union of 

 the different parts which compose the body of 

 the sternum, it is necessary to make a distinc- 

 tion between the lateral conjunction that is, 

 the union of the osseous points which are 

 situated on each side of the median line 

 and the vertical conjunction, or the union of 

 the pieces of the sternum properly so called. 

 The lateral conjunction, or the union of these 

 osseous germs, which form a pair in the same 

 interval, always precedes the vertical conjunc- 

 tion. 



The vertical conjunction, or the union of 

 the different pieces of the body of the sternum 



* Cruveilhier, Descrip. Anat. 8vo. 1840. Loncl. 

 p. 87. 



f Recherches sur Differentes Pieces du Sque- 

 lette des Animaux Vertebres, &c. in " Annales des 

 Sciences Naturelles." 2de Serie, t. 10. (Zoologie) 

 p. 91. 



together, commences with the two inferior 

 portions. After this union, the body of the 

 bone consists only of three parts. The 2nd 

 piece then unites with the lower: the sternal 

 foramen is formed sometimes at the junction 

 of these last mentioned parts, sometimes at 

 the place where the two lateral points of the 

 4th and of the 3rd portions of the body are 

 united. If the interruption to the progress 

 of ossification should occur at the point where 

 the lateral parts of two sternal pieces would 

 meet, the foramen is likely to have con- 

 siderable size ; for it may be the result of an 

 "arrest of development" proceeding from 

 four centres each constituting a part. (Fig. 660. 

 d.) The union of the divisions of the body 

 of the sternum takes place precisely in the 

 inverse order of their appearance In fact 

 the appearance of the osseous points proceeds 

 from above downwards, while their union 

 proceeds from below upwards : a fact which 

 verifies the assertion, that the order of 

 development of osseous points is not always 

 correlative to the order of junction. 



The lowest or 5th piece is joined to the 

 4th soon after puberty ; the 4th and 

 the 3rd are united, between 20 and 30 

 years of age ; and the body of the sternum 

 is usually not completed by the junction 

 of the 3rd piece to the 2nd before 35 or 40 

 years. Lastly, the 1st division does not in 

 general join the rest of the sternum at any 

 period ; but should its union happen to take 

 place, it is only to be met with in advanced 

 age. 



Of the ossification of the appendix. This is 

 generally accomplished by one nodule. Some- 

 times there are two ; and then they are rarely 

 symmetrical. The process commences in the 

 upper part of the cartilage, and very rare'y 

 extends through the whole. The time of ap- 

 pearance of the osseous point is extremely 

 variable. Sometimes it is visible towards the 

 3rd or 4th year; sometimes not until the 

 12th or even the 18th year; according to 

 the observation of Beclard, between the 2nd 

 and 18th years. 



From the 40th to the 50th year, and some- 

 times later, the appendix becomes united to 

 the body of the sternum. From the varieties 

 of ossification or development of the sternum, 

 it will be evident that it is impossible to assign 

 to it a limited number of osseous points. 



OF THR RIBS. The ribs (Costcs from ens- 

 todcs *) extend from the dorsal portion of 

 the vertebral column to the sternum, form- 

 ing arches which correspond to the lateral 

 segments of the chest. About one sixth of 

 the ribs are cartilaginous, and the rest os- 

 seous. The osseous portion is the rib pro- 

 perly so called ; the cartilaginous portion is 

 named the costal cartilage. 



The ribs are 24 in number, 12 on each 

 side ; but cases occasionally occur in which 

 this number is augmented by the addition 



* As if they were guardians of those principal 

 organs of the animal machine, the heart and lungs. 

 Munro: The Anatomy of the Human Bones, 

 p. 234. Edingb. 1726. 



