416 PROCEEDINGS OF THE ACADEMY OP 



On the Notation of the Bibs. Dr. Allen presented the follow- 

 ing argument : 



The rib is a member of a system of arches which are arranged 

 bilaterally, each vertebra having a single pair. 



The vertebral end of each dorsal rib bears a facet articulating 

 with its own vertebra. When the end bears two facets the lower 

 one articulates with its own vertebra, while the upper articulates 

 with the vertebra above it. The latter facet may be termed a 

 secondary one, and has no homological value. 



Now this method of arrangement of the facets must be true when 

 applied to the sternal end of the rib through its produced chon- 

 dral segment, the costal cartilage, so that the segment of the 

 sternum bears a strict relation of sequence to the dorsal vertebrae; 

 each segment corresponding to a right and left rib. Thus the 

 first rib belongs to the manubrium, and may be called the ma- 

 nubrial rib. The second, although placed apparently between the 

 manubrium and gladiolus, is named by the position of its lower 

 attachment a gladiolar rib. In the young, the succeeding segments 

 of the gladiolus can be named in the same order as far as the 

 fourth. Be3 T ond this the remaining ribs are so crowded that ana- 

 lysis of them is impossible. It can be seen, however, by studying 

 the arrangement in quadrupeds, that the rule holds good, each rib 

 owning, in a homological sense, its own sternal segment. For the 

 present purpose all that remains of importance is to accept as a lead- 

 ing thought, that when a rib is seen joining any two segments of 

 the sternum to refer it to the lower of the two. Thus, when the 

 seventh rib is seen joining the sternum at the xipho-gladiolar 

 junction, it is correct to assign the rib not to the gladiolus but to 

 the xyphoid cartilage, and, placing it there, we remove it from the 

 series of the gladiolar ribs. 



Now the manubrial and the gladiolar ribs are the true ribs 

 and these, with the removal of the seventh, are but six in number. 

 It will also be seen that were all the false ribs produced they 

 would be xyphoidal ribs. 



It is commonly the case that where a rule of notation is estab- 

 lished itwillbe found to be correlative with details both of structure 

 and of function. This is the case in the example above cited. 

 The ribs (first 6) which present concave upper borders, and have a 

 vertical surface at the pulmonary groove, are the true or manu- 

 brio-gladiolar ribs, and are those which ascend in inspiration. 



The ribs (last (!) which present convex upper borders, and yield 

 in the pulmonary groove a surface inclined downward and forward, 

 are the xyphoidal ribs (or which if produced would be xyphoidal) 

 and are those which descend in inspiration. 



It will be seen that both sets present borders concave to the 

 line of traction of the muscles acting upon them. 



