THESE _Bones_ call’d _Innominata_ are of wonderful _Use_ and _Service_: For besides that they form the _PELVIS_, and defend every Part of its _Contents_, they also give _Connexion_ and _Juncture_ of the rest of the Body, to the _Thigh-Bones_; as they likewise give _Rise_ and _Origin_ to many MUSCLES, and are the _Basis_ of Support of the SPINE of the _Back_, as well as of all the _Superior Parts_. Whence I come _à propos_ to descant a little upon this particular _Part_, as far as concerns our present Purpose.
THE SPINE then is that _Bony Column_ or _Ridge_, which extends itself down the _Back_ from the HEAD to the _Fundament_, containing the _Spinal Marrow_, and resembling the _Letter_ S in figure.
IN This SPINA therefore we must consider its _Fivefold Division_; namely, into NECK, BACK, LOINS, OS SACRUM, and OS COCCYGIS. The First _Three_ consist of 24 VERTEBRÆ; whereof the _Neck_ has 7, the _Back_ 12, and 5 belong to the _Loins_. _Those_ of the NECK bend _inwards_; those of the BACK _outwards_, for enlarging the _Cavity_ of the THORAX; _Those_ of the LOINS bend _inwards_ again; and _Those_ of the OS SACRUM _outwards_, to enlarge the _Cavity_ of the _PELVIS_.
THE VERTEBRÆ of the _two last_ concern us most in this Place; wherefore I shall say no more of the _rest_, save only by the By, or coincidently, as they fall in my way. _Those_ of the LOINS then are the _Thickest_ and _Broadest_, and the _Last_ of them is the _Largest_ of all the VERTEBRÆ; as their _Cartilages_ are thicker and stronger than any of the _Others_, and their _Acute Processes_ are at a greater _Distance_ from one another. From whence it comes to pass, that the greatest _Motion_ of the BACK is perform’d by the VERTEBRÆ of the LOINS.
THE VERTEBRÆ of the OS SACRUM grow so close together in _Adults_, that they make but one large solid _BONE_, of a _Triangular Figure_; and yet not without the _Mark_ of a four or five-fold _Division_: As in CHILDREN, it consists of many more _Pieces_ or _Divisions_. However, its _Basis_ is tyed to the last VERTEBRÆ of the LOINS, and the _Upper part_ of its _Sides_ to the ILIA; as its _Point_ is to the OS COCCYGIS.
THE OS COCCYGIS is also in _Adults_, for the most part, but one entire _BONE_; tho’ in _younger Persons_ it is compos’d of 3 or 4 small _Divisions_; Of which the _Lower_ is still less than the _Upper_; till the _Last_ ends in a small _Cartilage_. It is join’d in its _Glenoide Cavity_ to the Extremity of the OS SACRUM; being short and bent _inwards_: It supports the INTESTINUM RECTUM, and yields to the _Pressure_ of the _INFANT_ in _Travail_: But _MIDWIVES_ ought not to thrust it back or repel it with _Violence_; No, they should rather handle it _gently_, if they would prevent dangerous _Consequences_, as well as great _Pain_ to the _Woman_ in _LABOUR_.