158 THOMPSON YATES LABORATORIES REPORT 
the knee, combined with flexion of hip and ankle, is frequently followed by, and gives way to, 
extension of knee, hip, and ankle ; extension at hip is perhaps the most frequent of these extensions. 
It is noteworthy that in Cat, as I previously pointed out in Frog,* the extension is rapid in onset, 
short in duration, and rapid in disappearance — a kick in fact — as compared with the contraction 
in the flexors. 
For instance, following flexion of the knee, extension frequently occurs in the march of 
the spinal reflex, started from a pinch of the idio-lateral foot ; similarly, it may rapidly follow 
extension of the hip ; or, as a crossed reflex, it may follow and accompany flexion of hip and knee 
of the opposite side, and in this last case may initiate an alternating 'extension-flexion' reflex in the 
limb of its own side. The relation between the neurons of extensors and flexors at elbow is much 
the same as between those of extensors and flexors at knee, the flexors of elbow corresponding 
with flexors at knee. But the diflPerence between flexors and extensors at elbow does not seem 
to be quite so pronounced as between flexors and extensors at knee. In its behaviour in spinal 
reflexes, the brachial triceps resembles the extensors of the knee, also in its crossed relation with 
the flexors of the opposite elbow. In the Cat, contraction of the triceps brachii, as a primary 
idiolateral local reflex, is rare, but it is quite usually occurrent as the primary contraction of the 
crossed fore-limb, while contraction of the flexors of elbow is the primary contraction in the 
homonymous fore-limb. But I have seen flexion of the opposite elbow occur on rare occasions 
in response to strong excitation of the fore-paw of one side in the Cat. 
In the Rabbit, extension of the knee is still rarer as the primary movement of a spinal reflex 
than even in Cat and Dog, but, on account of the relatively slight depression caused by spinal 
transection in the Rabbit, it is a very frequent movement in the course of the ' march ' of a spinal 
reflex. It does not, however, occur nearly so frequently — in fact, I have never yet seen it occur 
as the initial movement of the crossed side in the Rabbit — for in Rabbit, flexion of the knee and 
hip seem the primary crossed just as they are the primary idio-lateral reflexes. This is in obvious 
relation to the mode of progression of the animal. Thus, in Rabbit, a pinch of the tail will 
cause symmetrically bilateral flexions, followed by extensions of the hind-limbs, although in the 
fore-limbs flexion of one fore-limb occurs with extension of the opposite fore-limb. Pinch of one 
foot will evoke flexion of the knees and hips of both sides, instead of flexion of idio-lateral and 
extension of contra-lateral knee, as is usual in the Cat. 
Long Intraspinal Paths 
Throughout the course of the above, I have refrained, as far as might be, from reference to 
reflexes of long intraspinal path. The functional regions of the cord may, for convenience, be 
considered right and left of (i) neck, (2) fore-limb, (3) trunk, (4) hind-limb, and (5) tail (see p. 
139). By a 'long intraspinal path,' I mean one which connects together any two of the said 
regions without involving cerebellum or cerebrum. 
Examples of reflexes involving long intraspinal paths are : — 
Cat : — Spinal transection above Ilnd cervical level : compressing left fore-paw between fingers 
* ' Lumbo-sacral Plexus,' 'Journ. of Physiol.,' 13, 1892.' 
