Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 16 On the Vertebrae of the Thorax

The difference between ascending and descending processes, and their system of articulation

The system of articulation of all vertebrae above the sacrum, accomplished by the processes just mentioned, is double: either the vertebra beneath goes up into the one above and is received by it, or the one beneath receives the one above in its depressions. Thus every vertebra, with only two exceptions, receives on one end and is received on the other. The first cervical vertebra receives on its upper and lower sides: on its upper [facies articularis superior] it receives the capitula [condylus occipitalis] of the occipital bone (N in fig. 2, ch. 15 receives B in fig. 1), and on its lower [facies articularis inferior] it receives the second cervical vertebra (Y in fig. 4, ch. 15 receives c [facies articularis superior] in fig. 5). 46 The twelfth thoracic (unless there is an extra vertebra) is received on both sides and receives none (D in the figure for chapter 14, and next to the 12th rib in the third skeletal figure). All the vertebrae above it as far as the first cervical are joined by the first type of articulation [processus articularis]: the upper vertebra always receives the lower, as the tenth thoracic receives the eleventh. 47 The vertebrae beneath the one which is received on both sides receive the vertebra above them on their upper surface, and on their lower enter into the vertebra beneath; this is the way the first lumbar vertebra is received by the second. 48 The thoracic vertebrae above the one received on either side have the same type of articulation in ascending and descending processes as the neck vertebrae (b in fig. 7, ch. 15, then d in fig. 9 and b, d in fig. 11). According to Galen in De ossibus, these are the nine upper thoracic vertebrae; or elsewhere, in De usu partium, the ten upper thoracic, for in the latter he says the eleventh

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and in the former the tenth thoracic, as he observed in apes and dogs. 49 But I have never seen the tenth received on both sides in man: it is most often the twelfth. Sometimes, when I have found a sacrum consisting of only five bones, I discovered the eleventh received on both sides, and at Bologna we assembled the bones of a French priest 50 whose first lumbar vertebra was received on both sides, and it had its transverse 51 processes articulated to itself just as the twelfth thoracic vertebra articulates to the twelfth ribs. Since, then, the twelfth thoracic appears most often to be received on both sides, let us base our account on this. Ascending processes (T, V in fig. 1) protrude from eleven thoracic vertebrae, and in the outer or posterior surface (X, Y in figs. 2 and 3) they are coated with a cartilage [c. articularis] in a noteworthy roundish area. The convexity of these processes [p. articularis superior] is so slight and flat that you can scarcely tell whether it should be considered a depression or a swelling. 52 The descending processes [p. articularis inferior] also possess a large depression [fovea costalis inferior] on their inner or anterior surface (c in figure 1) where they face the foramen cut out for the dorsal medulla, also more or less round 53 and coated with cartilage, corresponding exactly to the convexity just mentioned. These depressions and swellings differ from the depressions and swellings of the neck vertebrae only in their direction. The depressions and swellings of the neck vertebrae extend obliquely upward from the anterior, or obliquely downward from the other direction. It makes no difference whether you say they run upward or downward as long as you understand their obliquity and compare their position with that of the depressions and swellings of the thoracic vertebrae, which are more or less vertical as the structure of the thoracic vertebrae is stiffer and more resistant to movement. Since therefore the ascending processes of the thoracic vertebrae, like those of the neck, protrude on their posterior surface while the descending processes are hollowed out on their inner surface, the ascending processes of the lower vertebra naturally fit up into the descending processes of the upper vertebra, and the lower vertebra is taken in by the upper.

The course of the processes of the neck vertebrae is measured from a to b, of the thoracic from c to d.

Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 16 On the Vertebrae of the Thorax